BUG: Fix imported target config guess

When an IMPORTED target provides no generic configuration and no match
for a desired configuration then we choose any available configuration.
This change corrects the choice when the first listed available
configuration does not really have a location.

Source/cmTarget.cxx

@@ -3565,7 +3565,7 @@ void cmTarget::ComputeImportInfo(std::string const& desired_config,
         !loc && aci != availableConfigs.end(); ++aci)
       {
       suffix = "_";
-      suffix += cmSystemTools::UpperCase(availableConfigs[0]);
+      suffix += cmSystemTools::UpperCase(*aci);
       std::string locProp = "IMPORTED_LOCATION";
       locProp += suffix;
       loc = this->GetProperty(locProp.c_str());