Trim search operand from the end until URI decoding succeeds

Fixes #1137.

(imported from commit a23219d2cefdc2b739a165c88780fba409d4d878)

zephyr/static/js/narrow.js

@@ -51,7 +51,7 @@ function encodeOperand(operand) {
 }
 
 function decodeOperand(encoded) {
-    return decodeURIComponent(encoded.replace(/\+/g, ' '));
+    return util.robust_uri_decode(encoded.replace(/\+/g, ' '));
 }
 
 /* Convert a list of operators to a string.

zephyr/static/js/util.js

@@ -202,5 +202,23 @@ exports.same_sender = function util_same_sender(a, b) {
             (a.sender_email === b.sender_email));
 };
 
+// Avoid URI decode errors by removing characters from the end
+// one by one until the decode succeeds.  This makes sense if
+// we are decoding input that the user is in the middle of
+// typing.
+exports.robust_uri_decode = function (str) {
+    var end = str.length;
+    while (end > 0) {
+        try {
+            return decodeURIComponent(str.substring(0, end));
+        } catch (e) {
+            if (!(e instanceof URIError))
+                throw e;
+            end--;
+        }
+    }
+    return '';
+};
+
 return exports;
 }());