Cleanup: add "unreachable" message to "assert False" statements

Clarify that these blocks are unreachable so the intention is clear
if they're ever encountered.

scripts/modules/bpy_extras/io_utils.py

@@ -297,7 +297,7 @@ def axis_conversion(from_forward='Y', from_up='Z', to_forward='Y', to_up='Z'):
     for i, axis_lut in enumerate(_axis_convert_lut):
         if value in axis_lut:
             return Matrix(_axis_convert_matrix[i])
-    assert 0
+    assert False, "unreachable"
 
 
 def axis_conversion_ensure(operator, forward_attr, up_attr):

scripts/presets/keyconfig/keymap_data/blender_default.py

@@ -768,7 +768,7 @@ def km_window(params):
                 ("wm.search_menu", {"type": 'SPACE', "value": 'PRESS'}, None),
             )
         else:
-            assert False
+            assert False, "unreachable"
 
     return keymap
 
@@ -3530,7 +3530,7 @@ def km_frames(params):
                 ("screen.animation_play", {"type": 'SPACE', "value": 'PRESS'}, None),
             )
         else:
-            assert False
+            assert False, "unreachable"
 
         items.extend([
             ("screen.animation_play", {"type": 'SPACE', "value": 'PRESS', "shift": True, "ctrl": True},

scripts/startup/bl_operators/wm.py

@@ -2959,7 +2959,7 @@ class WM_OT_batch_rename(Operator):
                 elif method == 'SUFFIX':
                     name = name + text
                 else:
-                    assert 0
+                    assert False, "unreachable"
 
             elif ty == 'STRIP':
                 chars = action.strip_chars
@@ -3004,9 +3004,9 @@ class WM_OT_batch_rename(Operator):
                 elif method == 'TITLE':
                     name = name.title()
                 else:
-                    assert 0
+                    assert False, "unreachable"
             else:
-                assert 0
+                assert False, "unreachable"
         return name
 
     def _data_update(self, context):