Mono: Fix domain reload never triggering

modules/mono/csharp_script.cpp

@@ -647,6 +647,8 @@ void CSharpLanguage::reload_assemblies_if_needed(bool p_soft_reload) {
 			name = "UnnamedProject";
 		}
 
+		name += ".dll";
+
 		if (proj_assembly) {
 			String proj_asm_path = proj_assembly->get_path();