[apps/editor_controller] Fix backspace handling in text area

The editor controller handles backspace if it is at the beginning of a
line, to remove multiple spaces to match the indentation, but it should
not do so if there is an ongoing selection

escher/include/escher/text_input.h

@@ -16,6 +16,7 @@ public:
   bool setCursorLocation(const char * location);
   virtual void scrollToCursor();
   // Selection
+  bool selectionIsEmpty() const { return nonEditableContentView()->selectionIsEmpty(); }
   void resetSelection() { contentView()->resetSelection(); }
   void deleteSelection();
   // Alignment