MinPlatformPkg/TestPointCheckLib: Add check for pointers

In DxeCheckBootVariable.c, add check for BootOrder and Variable
in the if statement.
In DxeCheckGcd.c, add check for GcdIoMap to ensure it not NULL
when allocating memory to what it points to.

Cc: Michael Kubacki <michael.a.kubacki@intel.com>
Cc: Chasel Chiu <chasel.chiu@intel.com>
Cc: Nate DeSimone <nathaniel.l.desimone@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Signed-off-by: Shenglei Zhang <shenglei.zhang@intel.com>
Reviewed-by: Chasel Chiu <chasel.chiu@intel.com>