Merge pull request #4894 from CodingFabian/optimize-jpgjs-receiveAndExtend

Optimize JPG.js receiveAndExtend for 1 bit case.

src/core/jpg.js

@@ -159,6 +159,9 @@ var JpegImage = (function jpegImage() {
     }
 
     function receiveAndExtend(length) {
+      if (length === 1) {
+        return readBit() === 1 ? 1 : -1;
+      }
       var n = receive(length);
       if (n >= 1 << (length - 1)) {
         return n;