Fix glitch entering tag with whitespace

If an existing colored tag was added to an item with whitespace around it, the
tag didn't immediately show up with a color.

chrome/content/zotero/bindings/tagsbox.xml

@@ -638,6 +638,7 @@
 					var tabindex = textbox.getAttribute('ztabindex');
 					
 					var oldValue = textbox.getAttribute('value');
+					textbox.value = textbox.value.trim();
 					var value = textbox.value;
 					
 					var tagsbox = Zotero.getAncestorByTagName(textbox, 'tagsbox');