MAINT-6911 Fixes viewer crash after using "Clear settings & reset form"

doc/contributions.txt

@@ -205,6 +205,7 @@ Ansariel Hiller
 	MAINT-6752
 	MAINT-6773
 	MAINT-6906
+	MAINT-6911
 	STORM-2140
 Aralara Rajal
 Arare Chantilly

indra/newview/llfloatermodeluploadbase.cpp

@@ -80,6 +80,7 @@ void LLFloaterModelUploadBase::requestAgentUploadPermissionsCoro(std::string url
     if (!observer)
     { 
         LL_WARNS("MeshUploadFlag") << "Unable to get observer after call to '" << url << "' aborting." << LL_ENDL;
+        return;
     }
 
     if (!status)