trying another possibility

intl/uconv/src/nsConverterInputStream.cpp

@@ -245,7 +245,8 @@ nsConverterInputStream::Fill(nsresult * aErrorCode)
       NS_ASSERTION(0 < mUnicharData->GetBufferSize() - mUnicharDataLength,
                    "Decoder returned an error but filled the output buffer! "
                    "Should not happen.");
-      mUnicharData->GetBuffer()[mUnicharDataLength++] = mReplacementChar;
+      mUnicharData->GetBuffer()[mUnicharDataLength++] =
+                                             PRUnichar(mReplacementChar);
       ++srcConsumed;
       // XXX this is needed to make sure we don't underrun our buffer;
       // bug 160784 again

intl/uconv/src/nsConverterInputStream.h

@@ -88,7 +88,7 @@ class nsConverterInputStream : public nsIConverterInputStream,
     PRUint32  mLeftOverBytes;
     PRUint32  mUnicharDataOffset;
     PRUint32  mUnicharDataLength;
-    PRUnichar mReplacementChar;
+    PRUint32  mReplacementChar;
 
     nsLineBuffer<PRUnichar>* mLineBuffer;    
 };