[orca/gnome-3-38] Fix crash when generating speech for childless math element

[Joanmarie Diggs <joanied src gnome org>]

commit 89d41489ef68bc154e58701f0172d8f98ec2e660
Author: Joanmarie Diggs <jdiggs igalia com>
Date:   Thu Dec 3 17:34:05 2020 +0100

    Fix crash when generating speech for childless math element

 src/orca/speech_generator.py | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)
---
diff --git a/src/orca/speech_generator.py b/src/orca/speech_generator.py
index 8a635ef69..cdba115b2 100644
--- a/src/orca/speech_generator.py
+++ b/src/orca/speech_generator.py
@@ -2510,7 +2510,10 @@ class SpeechGenerator(generator.Generator):
 
     def _generateMath(self, obj, **args):
         result = []
-        children = [child for child in obj] or [obj]
+        children = [child for child in obj]
+        if not children and not self._script.utilities.isMathTopLevel(obj):
+            children = [obj]
+
         for child in children:
             if self._script.utilities.isMathLayoutOnly(child) and child.childCount:
                 result.extend(self._generateMath(child))