Fix regression introduced in v1.0.6 (#3993) where subtitle track segm…

…ent loading at position less than target duration only loads the first segment

(only appears in streams with irregularly large target durations compared to segment duration)

src/utils/buffer-helper.ts

@@ -91,6 +91,7 @@ export class BufferHelper {
     end: number;
     nextStart?: number;
   } {
+    pos = Math.max(0, pos);
     // sort on buffer.start/smaller end (IE does not always return sorted buffered range)
     buffered.sort(function (a, b) {
       const diff = a.start - b.start;