Revert "Only do formula class sanity checks once"

This reverts commit ace78b1f3a59a893c7068e485555acf792470080.

Fixes Homebrew/homebrew#30154.

Library/Homebrew/formulary.rb

@@ -59,9 +59,7 @@ class Formulary
         raise FormulaUnavailableError.new(name)
       end
 
-      if have_klass
-        Formulary.get_formula_class(class_name)
-      else
+      unless have_klass
         STDERR.puts "#{$0} (#{self.class.name}): loading #{path}" if ARGV.debug?
         begin
           require path
@@ -73,13 +71,13 @@ class Formulary
           raise if ARGV.debug?  # let's see the REAL error
           raise FormulaUnavailableError.new(name)
         end
+      end
 
-        klass = Formulary.get_formula_class(class_name)
-        if klass == Formula || !(klass < Formula)
-          raise FormulaUnavailableError.new(name)
-        end
-        klass
+      klass = Formulary.get_formula_class(class_name)
+      if klass == Formula || !(klass < Formula)
+        raise FormulaUnavailableError.new(name)
       end
+      klass
     end
   end