file_manager: raise new InvalidStreamURLError if the URL is invalid

When using `lbrynet get URL`, if the URL is not a valid URL
the function `url.URL.parse` will raise a `ValueError` exception
which will produce a whole backtrace.

For example, this is the case if we provide a channel name
with a forward slash but without a stream name.
```
lbrynet get @Non-existing/
```

```
Traceback (most recent call last):
  File "/opt/git/lbry-sdk/lbry/file/file_manager.py", line 84, in download_from_uri
    if not URL.parse(uri).has_stream:
  File "/opt/git/lbry-sdk/lbry/schema/url.py", line 114, in parse
    raise ValueError('Invalid LBRY URL')
ValueError: Invalid LBRY URL
WARNING  lbry.extras.daemon.daemon:1110: Error downloading Non-existing/: Invalid LBRY URL
```

Now we raise a new `InvalidStreamURLError` which can be trapped in the upper functions
that use `url.URL.parse` such as `FileManager.download_from_uri`.
If we do this the traceback won't be shown.
```
WARNING  lbry.file.file_manager:252:
Failed to download Non-existing/: Invalid LBRY stream URL: '@Non-existing/'
WARNING  lbry.extras.daemon.daemon:1110:
Error downloading Non-existing/: Invalid LBRY stream URL: '@Non-existing/'
```

This handles the case when trying to download only "channel" parts
without the claim part.
```
lbrynet get @Non-existing
lbrynet get @Non-existing/
lbrynet get Non-existing/
```

lbry/error/README.md

@@ -38,6 +38,7 @@ Code | Name | Message
 114 | InputStringIsBlank | {argument} cannot be blank.
 115 | EmptyPublishedFile | Cannot publish empty file: {file_path}
 116 | MissingPublishedFile | File does not exist: {file_path}
+117 | InvalidStreamURL | Invalid LBRY stream URL: '{url}' -- When an URL cannot be downloaded, such as '@Channel/' or a collection
 **2xx** | Configuration | Configuration errors.
 201 | ConfigWrite | Cannot write configuration file '{path}'. -- When writing the default config fails on startup, such as due to permission issues.
 202 | ConfigRead | Cannot find provided configuration file '{path}'. -- Can't open the config file user provided via command line args.

lbry/error/__init__.py

@@ -105,6 +105,16 @@ class MissingPublishedFileError(InputValueError):
         super().__init__(f"File does not exist: {file_path}")
 
 
+class InvalidStreamURLError(InputValueError):
+    """
+    When an URL cannot be downloaded, such as '@Channel/' or a collection
+    """
+
+    def __init__(self, url):
+        self.url = url
+        super().__init__(f"Invalid LBRY stream URL: '{url}'")
+
+
 class ConfigurationError(BaseError):
     """
     Configuration errors.

lbry/file/file_manager.py

@@ -5,6 +5,7 @@ from typing import Optional
 from aiohttp.web import Request
 from lbry.error import ResolveError, DownloadSDTimeoutError, InsufficientFundsError
 from lbry.error import ResolveTimeoutError, DownloadDataTimeoutError, KeyFeeAboveMaxAllowedError
+from lbry.error import InvalidStreamURLError
 from lbry.stream.managed_stream import ManagedStream
 from lbry.torrent.torrent_manager import TorrentSource
 from lbry.utils import cache_concurrent
@@ -81,8 +82,11 @@ class FileManager:
         payment = None
         try:
             # resolve the claim
+            try:
                 if not URL.parse(uri).has_stream:
-                raise ResolveError("cannot download a channel claim, specify a /path")
+                    raise InvalidStreamURLError(uri)
+            except ValueError:
+                raise InvalidStreamURLError(uri)
             try:
                 resolved_result = await asyncio.wait_for(
                     self.wallet_manager.ledger.resolve(
@@ -244,7 +248,7 @@ class FileManager:
             raise error
         except Exception as err:  # forgive data timeout, don't delete stream
             expected = (DownloadSDTimeoutError, DownloadDataTimeoutError, InsufficientFundsError,
-                        KeyFeeAboveMaxAllowedError)
+                        KeyFeeAboveMaxAllowedError, ResolveError, InvalidStreamURLError)
             if isinstance(err, expected):
                 log.warning("Failed to download %s: %s", uri, str(err))
             elif isinstance(err, asyncio.CancelledError):