Bug 1470355 - Firefox is unresponsive when visiting https://www.youtube.com/premium, r=valentin

This patch avoids returning NS_BASE_STREAM_WOULD_BLOCK from CacheFileInputStream::ReadSegments when it was called with aCount=0.

netwerk/cache2/CacheFileInputStream.cpp

@@ -152,6 +152,10 @@ CacheFileInputStream::ReadSegments(nsWriteSegmentFun aWriter, void *aClosure,
     return NS_OK;
   }
 
+  if (aCount == 0) {
+    return NS_OK;
+  }
+
   EnsureCorrectChunk(false);
 
   while (true) {