[FragmentLoader] Fix edge case for LOADING_IN_PROGRESS

Unsure if this is correct fix, but there was an edge case where leveling up immediately after first (test) Fragment caused infinite loop if that level up Fragment was determined to take too long to load, which is a strange considering that metrics determined that it was possible to load that Fragment.

Author: hparra

src/com/pivotshare/hls/loader/FragmentLoader.as

@@ -372,7 +372,7 @@ package com.pivotshare.hls.loader {
  * loading to determine if we should stay at current bitrate.
  */
  case LOADING_IN_PROGRESS:
- if(_hls.autoLevel && _fragCurrent.level) {
+ if(_hls.autoLevel && _fragCurrent.level && _fragmentFirstLoaded) {
 
  // monitor fragment load progress after half of expected fragment duration,to stabilize bitrate
  var requestDelay : int = getTimer() - _metrics.loading_request_time;