Clean up label generation

Only check for localness when we already know we have a local

test/asm/sym-scope.asm

@@ -0,0 +1,21 @@
+SECTION "Scopes", ROM0
+
+; Neither of these should be created
+.tooSoon
+Nice.try
+
+Parent:
+.loc
+	dw Parent.loc ; This is what it should expand to
+Parent.explicit
+	dw .explicit ; This should expand to the above
+
+
+; None of the two locals below should manage to be created, being in the wrong scopes
+; Note however that `Parentheses` begins with `Parent`, which string checks may fail to handle
+
+Parentheses.check
+
+Parentheses:
+
+Parent.check