Remove more superfluous if(p) checks around free(p)

This patch has been generated by the following Coccinelle semantic patch:

@@
expression E;
@@

-if(E) { free(E); }
+free(E);

Signed-off-by: Mikhail Gusarov <dottedmag@dottedmag.net>
Reviewed-by: Julien Cristau <jcristau@debian.org>
Reviewed-by: Fernando Carrijo <fcarrijo@yahoo.com.br>
Reviewed-by: Matt Turner <mattst88@gmail.com>

hw/xwin/winerror.c

@@ -144,9 +144,7 @@ winMessageBoxF (const char *pszError, UINT uType, ...)
 	      MB_OK | uType);
 
  winMessageBoxF_Cleanup:
-  if (pszErrorF)
-    free(pszErrorF);
-  if (pszMsgBox)
-    free(pszMsgBox);
+  free(pszErrorF);
+  free(pszMsgBox);
 #undef MESSAGEBOXF
 }