tests: Fix buffer not cleaned up on test failure

tests/display/test_cg_shader.py

@@ -136,8 +136,8 @@ def run_cg_test(gsg, body, preamble="", inputs={},
         engine.render_frame()
     except AssertionError as exc:
         assert False, "Error executing shader:\n" + code
-
-    engine.remove_window(buffer)
+    finally:
+        engine.remove_window(buffer)
 
     # Download the texture to check whether the assertion triggered.
     triggered = tuple(result.get_ram_image())

tests/display/test_glsl_shader.py

@@ -213,8 +213,8 @@ def run_glsl_test(gsg, body, preamble="", inputs={}, version=420, exts=set(),
             engine.render_frame()
         except AssertionError as exc:
             assert False, "Error executing shader:\n" + code
-
-        engine.remove_window(buffer)
+        finally:
+            engine.remove_window(buffer)
 
     # Download the texture to check whether the assertion triggered.
     if use_compute: