Fixed bug where seeking forward in a (cached) HttpDataStream response

didn't work properly. This same bug may also cause weird behaviors
during playback if the engine probes beyond the end of the file, then
attempts to rewind the read head to recover

src/plugins/httpdatastream/HttpDataStream.cpp

@@ -196,7 +196,9 @@ class FileReadStream {
                 this->underflow.wait(lock);
             }
 
-            if (this->interrupted || this->Eof()) {
+            /* if we've been interrupted, or we know we're at EOF and have been asked
+            to read beyond it. */
+            if (this->interrupted || (position >= this->Position() && this->Eof())) {
                 return false;
             }