MdeModulePkg/RegularExpressionDxe: Miss null pointer check

Oniguruma https://github.com/kkos/oniguruma
this change is merged from oniguruma develop branch.
from commit ea36d810f1d9b28f3ef20bd8d453bea2f7fb598b

Cc: Liming Gao <liming.gao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Dongao Guo <dongao.guo@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>

MdeModulePkg/Universal/RegularExpressionDxe/Oniguruma/unicode.c

@@ -758,6 +758,10 @@ onig_unicode_define_user_property(const char* name, OnigCodePoint* ranges)
 
   if (UserDefinedPropertyTable == 0) {
     UserDefinedPropertyTable = onig_st_init_strend_table_with_size(10);
+    if (IS_NULL(UserDefinedPropertyTable)) {
+      xfree(s);
+      return ONIGERR_MEMORY;
+    }
   }
 
   e = UserDefinedPropertyRanges + UserDefinedPropertyNum;