ShellPkg: Fix the bug that handling Ctrl-C improperly
ShellPkg: Fix the bug that handling Ctrl-C improperly

Current implementation resets the CTRL-C event early when printing
the shell prompt, when user types "<CTRL-C>ls<ENTER>", "ls" command
is terminated immediately when starts.
It's not an expected behavior from users' perspective.
Correct way is to reset the CTRL-C event just before running the
command, which is a bit later than current point.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ruiyu Ni <9fa3a6894a36bca79e6a72ad65af5a5702efecd1@intel.com>
Reviewed-by: Jaben Carsey <2d4ee76b36e91bee3a58378b7538904eb027a616@intel.com>

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