fix +13786 tab sometimes deletes character before

node_modules/ace/lib/ace/editor.js

@@ -1486,7 +1486,7 @@ var Editor = function(renderer, session) {
             var indentString = lang.stringRepeat(" ", count);
         } else {
             var count = column % size;
-            while (line[range.start.column] == " " && count) {
+            while (line[range.start.column - 1] == " " && count) {
                 range.start.column--;
                 count--;
             }

node_modules/ace/lib/ace/editor_text_edit_test.js

@@ -124,6 +124,12 @@ module.exports = {
         var range = editor.getSelectionRange();
         assert.position(range.start, 1, 7);
         assert.position(range.end, 2, 7);
+        
+        session.setValue("   x");
+        session.setOption("useSoftTabs", false);
+        editor.selection.moveTo(0, 3);
+        editor.indent();
+        assert.equal("\tx", session.toString());
     },
 
     "test: indent selected lines" : function() {