Fixed 2 more casted lvalue issues.

dlls/avifil32/avifile.c

@@ -1115,7 +1115,7 @@ static HRESULT WINAPI IAVIStream_fnRead(IAVIStream *iface, LONG start,
 
       block++;
       offset = 0;
-      ((BYTE*)buffer) += size;
+      buffer = ((LPBYTE)buffer)+size;
       samples    -= size;
       buffersize -= size;
 

dlls/avifil32/editstream.c

@@ -1012,7 +1012,7 @@ static HRESULT WINAPI IEditAVIStream_fnRead(IAVIStream*iface,LONG start,
       if (bytesread != NULL)
         *bytesread += readBytes;
       if (buffer != NULL) {
-        (LPBYTE)buffer += readBytes;
+        buffer = ((LPBYTE)buffer)+readBytes;
         buffersize     -= readBytes;
       }
       start   += count;