prevent "enter/save" key callback if string is empty (#509)

Co-authored-by: SG <who.just.the.doctor@gmail.com>

applications/gui/modules/text_input.c

@@ -289,7 +289,7 @@ static void text_input_handle_ok(TextInput* text_input) {
             uint8_t text_length = strlen(model->text);
 
             if(selected == ENTER_KEY) {
-                if(model->callback != 0) {
+                if(model->callback != 0 && text_length > 0) {
                     model->callback(model->callback_context, model->text);
                 }
             } else if(selected == BACKSPACE_KEY) {