cmake-gui: Fix "extra" generator entries in drop-down list

Refactoring in commit v3.7.0-rc1~291^2~1 (Refactor extra generator
registration to use factories, 2016-07-20) accidentally switched
the order of the "extra - base" generator names to "base - extra".
Switch it back.  While this could affect all callers of the
`GetRegisteredGenerators` method, only cmake-gui actually used this
particular field.

Closes: #16359

Source/cmake.cxx

@@ -929,7 +929,7 @@ void cmake::GetRegisteredGenerators(
          gen != genList.end(); ++gen) {
       GeneratorInfo info;
       info.name = cmExternalMakefileProjectGenerator::CreateFullGeneratorName(
-        (*i)->GetName(), *gen);
+        *gen, (*i)->GetName());
       info.baseName = *gen;
       info.extraName = (*i)->GetName();
       info.supportsPlatform = false;