check that the conversion really succeeds even when wxMBConv_win32::WC2MB() is called with NULL buffer

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@48643 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/strconv.cpp

@@ -2426,9 +2426,7 @@ public:
             return wxCONV_FAILED;
         }
 
-        // if we were really converting, check if we succeeded
-        if ( buf )
-        {
+        // we did something, check if we really succeeded
         if ( flags )
         {
             // check if the conversion failed, i.e. if any replacements
@@ -2438,6 +2436,19 @@ public:
         }
         else // we must resort to double tripping...
         {
+            // first we need to ensure that we really have the MB data: this is
+            // not the case if we're called with NULL buffer, in which case we
+            // need to do the conversion yet again
+            wxCharBuffer bufDef;
+            if ( !buf )
+            {
+                bufDef = wxCharBuffer(len);
+                buf = bufDef.data();
+                if ( !::WideCharToMultiByte(m_CodePage, flags, pwz, -1,
+                                            buf, len, NULL, NULL) )
+                    return wxCONV_FAILED;
+            }
+
             wxWCharBuffer wcBuf(n);
             if ( MB2WC(wcBuf.data(), buf, n) == wxCONV_FAILED ||
                     wcscmp(wcBuf, pwz) != 0 )
@@ -2447,7 +2458,6 @@ public:
                 return wxCONV_FAILED;
             }
         }
-        }
 
         // see the comment above for the reason of "len - 1"
         return len - 1;