[IMP] specific: check if custom table exists

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

However, customers may remove that table in successive upgrade requests, making
the call to `rename_table` unnecessary and the extra entry in the migration
report wrong.

Part-of: #91

Author: Pirols

src/util/specific.py

@@ -5,7 +5,7 @@
 from .misc import _cached
 from .models import rename_model
 from .modules import rename_module
-from .pg import column_exists, rename_table
+from .pg import column_exists, rename_table, table_exists
 from .report import add_to_migration_reports
 
 _logger = logging.getLogger(__name__)
@@ -84,6 +84,10 @@ def rename_custom_table(
     custom_module=None,
     report_details="",
 ):
+    if not table_exists(cr, table_name):
+        _logger.warning("Table %r not found: skip renaming", table_name)
+        return
+
     rename_table(cr, table_name, new_table_name, remove_constraints=False)
 
     module_details = " from module '{}'".format(custom_module) if custom_module else ""