[mypyc] Fix relative imports in __init__.pys (#10543)

Fixes mypyc/mypyc#842

Author: Gobot1234

mypyc/irbuild/statement.py

@@ -165,6 +165,8 @@ def transform_import_from(builder: IRBuilder, node: ImportFrom) -> None:
     module_state = builder.graph[builder.module_name]
     if module_state.ancestors is not None and module_state.ancestors:
         module_package = module_state.ancestors[0]
+    elif builder.module_path.endswith("__init__.py"):
+        module_package = builder.module_name
     else:
         module_package = ''