[IMP] specific: check if custom model exists

When a custom model conflicts with a standard one we may choose to write a
specific fix, using the `rename_custom_model` util to rename it.

However, although unlikely, customers may remove that model in successive
upgrade requests, making the call to `rename_model` unnecessary and the extra
entry in the migration report wrong.

Part-of: #91

Author: Pirols

src/util/specific.py

@@ -47,6 +47,11 @@ def dispatch_by_dbuuid(cr, version, callbacks):
 
 
 def rename_custom_model(cr, model_name, new_model_name, custom_module=None, report_details=""):
+    cr.execute("SELECT 1 FROM ir_model WHERE model = %s", [model_name])
+    if not cr.rowcount:
+        _logger.warning("Model %r not found: skip renaming", model_name)
+        return
+
     rename_model(cr, model_name, new_model_name, rename_table=True)
     module_details = " from module '{}'".format(custom_module) if custom_module else ""
     add_to_migration_reports(