[SFU] Handle ConnectionError exception instead of MaxRetryError

When we introduced retries in #591, we expected to handle
the MaxRetryError exception. Instead, what appears to happen is the
MaxRetryError exception block isn't hit, and instead, we get a chain
of Exceptions that results in the underlying Exception being raised,
which is a ConnectionError.

As such, this commit changes the MaxRetryError block to a
ConnectionError block, thus returning a more descriptive message to the
end user. An early return is also added to avoid a UnboundLocalError
when trying to use fetchedData after the Exception was handled.

This addresses #663.

cogs/sfu/roads.py

@@ -131,11 +131,14 @@ async def cam(self, ctx: Context, cam: str = ""):
             fetchedData = self.httpRetrySession.get(camera, headers=self.headers)
             fetchedData.raise_for_status()
         except requests.exceptions.HTTPError:
-            await ctx.send(":warning: This webcam is currently unavailable!")
+            await ctx.send(
+                ":warning: This webcam is currently unavailable! Please try again later"
+            )
             # self.logger.error(exc_info=True)
             return
-        except requests.adapters.MaxRetryError:
-            await ctx.send(":warning: Unable to retrieve webcam image. Please try again.")
+        except requests.adapters.ConnectionError:
+            await ctx.send(":warning: Unable to retrieve webcam image! Please try again later.")
+            return
 
         if not fetchedData.content:
             # Make sure we don't fetch a zero byte file