Add support for older versions with bzlmod

Author: tempacc21

extension.bzl

@@ -4,14 +4,14 @@ load("@bazel_tools//tools/build_defs/repo:jvm.bzl", "jvm_maven_import_external")
 
 def get_root_module(module_ctx):
     for mod in module_ctx.modules:
-        if mod.is_root:
+        if mod.is_root and hasattr(mod.tags.client, "version"):
+            return mod
+    for mod in module_ctx.modules:
+        for tags in mod.tags.client:
             return mod
-    return None
 
 def _openapi_generator_impl(module_ctx):
     wanted_module = get_root_module(module_ctx)
-    if wanted_module == None:
-        wanted_module = module_ctx.modules[0]
 
     for install in wanted_module.tags.client:
         jvm_maven_import_external(