don't crash when trying to dump struct members which are NULL pointers

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@33092 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/debughlp.cpp

@@ -305,6 +305,12 @@ wxDbgHelpDLL::DumpField(PSYMBOL_INFO pSym, void *pVariable, unsigned level)
             break;
 
         case SYMBOL_TAG_DATA:
+            if ( !pVariable )
+            {
+                s = _T("NULL");
+            }
+            else // valid location
+            {
                 wxDbgHelpDLL::DataKind kind;
                 if ( !DoGetTypeInfo(pSym, TI_GET_DATAKIND, &kind) ||
                         kind != DATA_MEMBER )
@@ -346,6 +352,7 @@ wxDbgHelpDLL::DumpField(PSYMBOL_INFO pSym, void *pVariable, unsigned level)
                         s = DumpUDT(&sym, pVariable, level);
                         break;
                 }
+            }
 
             if ( !s.empty() )
             {
@@ -458,7 +465,16 @@ wxDbgHelpDLL::DereferenceSymbol(PSYMBOL_INFO pSym, void **ppData)
         // remove one level of indirection except for the char strings: we want
         // to dump "char *" and not a single "char" for them
         if ( ppData && *ppData && GetBasicType(pSym) != BASICTYPE_CHAR )
-            *ppData = (void *)*((DWORD_PTR *)*ppData);
+        {
+            DWORD_PTR *pData = (DWORD_PTR *)*ppData;
+
+            if ( ::IsBadReadPtr(pData, sizeof(DWORD_PTR *)) )
+            {
+                break;
+            }
+
+            *ppData = (void *)*pData;
+        }
     }
 
     return tag;