Fix a K9 error.Result of GetVariable2() function that may return NULL will be dereferenced.

Signed-off-by: Wu Jiaxin <jiaxin.wu@intel.com >
Reviewed-by: Fu Siyuan <siyuan.fu@intel.com>
Reviewed-by: Dong Guo <guo.dong@intel.com>

git-svn-id: svn://svn.code.sf.net/p/edk2/code/trunk/edk2/MdeModulePkg@14813 6f19259b-4bc3-4df7-8a09-765794883524
Clean the help string and hot key info if an empty form is painting.

Signed-off-by: Eric Dong <eric.dong@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>

git-svn-id: svn://svn.code.sf.net/p/edk2/code/trunk/edk2/MdeModulePkg@14815 6f19259b-4bc3-4df7-8a09-765794883524