[release/6.0] Fix null being passed to g_path_get_dirname when probing in wasm (#84740)

* [6.0-staging] Bump branding to 6.0.18 (#84596)

* Fix null being passed to g_path_get_dirname when probing in wasm

* Update src/mono/mono/metadata/native-library.c

Co-authored-by: Aleksey Kliger (λgeek) <akliger@gmail.com>

* Revert versioning changes brought from staging.

---------

Co-authored-by: Carlos Sánchez López <1175054+carlossanlop@users.noreply.github.com>
Co-authored-by: Katelyn Gadd <kg@luminance.org>
Co-authored-by: Aleksey Kliger (λgeek) <akliger@gmail.com>

Author: 4 people

src/mono/mono/metadata/native-library.c

@@ -529,7 +529,8 @@ netcore_probe_for_module (MonoImage *image, const char *file_name, int flags)
 		module = netcore_probe_for_module_variations (pinvoke_search_directories[i], file_name, lflags);
 
 	// Check the assembly directory if the search flag is set and the image exists
-	if (flags & DLLIMPORTSEARCHPATH_ASSEMBLY_DIRECTORY && image != NULL && module == NULL) {
+	if ((flags & DLLIMPORTSEARCHPATH_ASSEMBLY_DIRECTORY) != 0 && image != NULL && 
+		module == NULL && (image->filename != NULL)) {
 		char *mdirname = g_path_get_dirname (image->filename);
 		if (mdirname)
 			module = netcore_probe_for_module_variations (mdirname, file_name, lflags);