fixed a bug related to mod + Grave with combined ESC/Grave key

fixed a bug related to mod + Grave with combined ESC/Grave key

This only applies to keymaps that has combined esc/grave. Here we call it theKEY.
Think about the motion when we do shift + theKEY (typing ~), or CMD + theKEY (switching window on MAC). Based on the original code, we must do following sequence:  press shift -> press theKEY -> release theKEY -> release shift. However, it is very possible and natural that we do this stroke sequence instead: press shift -> press theKEY -> release shift -> release theKEY.

If we do the 2nd stroke sequence, the code will del_key(ESC) instead of (GRV) when we release theKEY. This caused some inconvenient issues and ghost typing.

By adding a flag, this issue is eliminated and will not affect any other functions.