Fix CompUnit::PrecompilationUnit::File::bytecode not returning bytecode

Since commit 81ac37f the bytecode method only
returned the bytecode when it wasn't already initialized.

src/core.c/CompUnit/PrecompilationStore/File.pm6

@@ -63,6 +63,7 @@ class CompUnit::PrecompilationStore::File
                     self!read-dependencies;
                     $!bytecode := $!handle.slurp(:bin,:close)
                 }
+                $!bytecode
             }
         }