Implement the bulk of the MPEG-TS demuxer, add a bunch of tests, and a few other things

src/reader.ts

@@ -20,6 +20,10 @@ export class Reader {
 			throw new InputDisposedError();
 		}
 
+		if (start < 0) {
+			return null;
+		}
+
 		if (this.fileSize !== null && start + length > this.fileSize) {
 			return null;
 		}
@@ -49,6 +53,10 @@ export class Reader {
 			throw new InputDisposedError();
 		}
 
+		if (start < 0) {
+			return null;
+		}
+
 		if (this.fileSize !== null) {
 			return this.requestSlice(
 				start,