Prevent JSON parsing errors

Bug: 61137
Change-Id: I2df6b6108bb7834b927205d3b6afa69354cecaf7

resources/js/ext.uls.preferences.js

@@ -180,8 +180,15 @@
 				this.preferences = preferenceStore().get( this.preferenceName );
 			} else {
 				var options = mw.user.options.get( this.preferenceName );
-				this.preferences = JSON.parse( options );
+
+				// Try to parse JSON
+				try {
+					this.preferences = JSON.parse( options );
+				} catch ( e ) {
+					this.preferences = {};
+				}
 			}
+
 			this.preferences = this.preferences || {};
 		},