vim-patch:8.1.0288: quickfix code uses cmdidx too often

Problem:    Quickfix code uses cmdidx too often.
Solution:   Add is_loclist_cmd(). (Yegappan Lakshmanan)
396659592f

src/nvim/ex_docmd.c

@@ -10139,6 +10139,17 @@ static void ex_folddo(exarg_T *eap)
   ml_clearmarked();      // clear rest of the marks
 }
 
+// Returns true if the supplied Ex cmdidx is for a location list command
+// instead of a quickfix command.
+bool is_loclist_cmd(int cmdidx)
+  FUNC_ATTR_PURE FUNC_ATTR_WARN_UNUSED_RESULT
+{
+  if (cmdidx < 0 || cmdidx > CMD_SIZE) {
+    return false;
+  }
+  return cmdnames[cmdidx].cmd_name[0] == 'l';
+}
+
 bool get_pressedreturn(void)
   FUNC_ATTR_PURE FUNC_ATTR_WARN_UNUSED_RESULT
 {