Fix badly computed output size in µBlock.base64.encode()

This bug could cause losing 1 to 3 bytes of information
dropped from various internal buffers at encoding time.

Possibly related feedback:
- https://www.reddit.com/r/uBlockOrigin/comments/cs1y26/

src/js/utils.js

@@ -544,7 +544,7 @@
     }
 
     encode(arrbuf, arrlen) {
-        const inputLength = arrlen >>> 2;
+        const inputLength = (arrlen + 3) >>> 2;
         const inbuf = new Uint32Array(arrbuf, 0, inputLength);
         const outputLength = this.magic.length + 7 + inputLength * 7;
         const outbuf = new Uint8Array(outputLength);