buffer-helper: correctly report bufferInfo when current time is locat…

…ed before buffered ranges, but within maxHoleDuration range

if media buffered : [10,40] , maxHoleDuration = 2s, and pos = 9s,
bufferInfo was
{ len : 31, start : 10, end : 40, nextStart : undefined }
whereas it should be
{ len : 0, start : 9, end : 9, nextStart : 10 }
we need to report the area as not buffered so that stream-controller will start loading fragment as needed

src/helper/buffer-helper.js

@@ -55,6 +55,12 @@ class BufferHelper {
         buffered2.push(buffered[i]);
       }
     }
+
+    // in case current position is located before buffered time ranges, report area as not buffered
+    if (buffered2.length && pos < buffered2[0].start) {
+      return {len: 0, start: pos, end: pos, nextStart : buffered2[0].start};
+    }
+
     for (i = 0, bufferLen = 0, bufferStart = bufferEnd = pos; i < buffered2.length; i++) {
       var start =  buffered2[i].start,
           end = buffered2[i].end;