Fix crash when ioproxy is passed to a plugin that doesn't support it (A…

…cademySoftwareFoundation#3453)

The plugin was freed before the error message printed that depends on
it.

src/libOpenImageIO/imageioplugin.cpp

@@ -565,10 +565,10 @@ ImageOutput::create(string_view filename, Filesystem::IOProxy* ioproxy,
     }
     if (out && ioproxy) {
         if (!out->supports("ioproxy")) {
-            out.reset();
             OIIO::pvt::errorfmt(
                 "ImageOutput::create called with IOProxy, but format {} does not support IOProxy",
                 out->format_name());
+            out.reset();
         } else {
             out->set_ioproxy(ioproxy);
         }