Allow trying to build forced-XML modules.

Ever since kde-projects XML support was added you could (in theory) use
the syntax +modulename on the command line to force kdesrc-build to
interpret that module as an XML module.

Later a filter was added to avoid building modules on typos, which also
trapped all +modules.

Now if you use +module on the command line kdesrc-build will keep
processing it, and catch misspellings later or build the whole module if
it's actually defined in kde_projects.xml.

kdesrc-build

@@ -3971,9 +3971,14 @@ sub expandModuleSets
 
     my $filter = sub {
         my $setName = $_->name();
+
         # If the module name matches a read-in Module, then it's not a set.
         return $_ if grep { $setName eq $_->name() } (@$knownModules);
 
+        # XML module can only happen if forced by user on command line, allow
+        # it.
+        return $_ if $_->type() eq 'proj';
+
         # Otherwise assume it's a set, replace this with all sub-modules in that
         # module set.
         my @modulesInSet = grep { $_->moduleSet() eq $setName } (@$knownModules);