cppcheck: small bool simplification

Found with duplicateConditionalAssign

Signed-off-by: Rosen Penev <rosenp@gmail.com>

src/xmp.cpp

@@ -622,12 +622,12 @@ void XmpParser::registeredNamespaces(Exiv2::Dictionary&) {
 
 void XmpParser::terminate() {
   XmpProperties::unregisterNs();
-  if (initialized_) {
 #ifdef EXV_HAVE_XMP_TOOLKIT
+  if (initialized_)
     SXMPMeta::Terminate();
-#endif
+#else
   initialized_ = false;
-  }
+#endif
 }
 
 #ifdef EXV_HAVE_XMP_TOOLKIT