Bug 1177541 - Remove warning if file is not found during deferred open. r=mcmanus

When doing a deferred open we should not emit a warning if the file is not
found. The proper return code is still returned.

netwerk/base/nsFileStreams.cpp

@@ -202,6 +202,11 @@ nsresult
 nsFileStreamBase::Read(char* aBuf, uint32_t aCount, uint32_t* aResult)
 {
     nsresult rv = DoPendingOpen();
+    if (rv == NS_ERROR_FILE_NOT_FOUND) {
+      // Don't warn if this is just a deferred file not found.
+      return rv;
+    }
+
     NS_ENSURE_SUCCESS(rv, rv);
 
     if (!mFD) {
@@ -489,6 +494,11 @@ NS_IMETHODIMP
 nsFileInputStream::Read(char* aBuf, uint32_t aCount, uint32_t* _retval)
 {
     nsresult rv = nsFileStreamBase::Read(aBuf, aCount, _retval);
+    if (rv == NS_ERROR_FILE_NOT_FOUND) {
+      // Don't warn if this is a deffered file not found.
+      return rv;
+    }
+
     NS_ENSURE_SUCCESS(rv, rv);
 
     // Check if we're at the end of file and need to close