[LyX/master] Fix endless loop in lyx2lyx reversion routine

[Juergen Spitzmueller]

commit 7e161a9d5d1331eb8fced35ef0fbb002fa30f60c
Author: Juergen Spitzmueller <spitz at lyx.org>
Date:   Mon Nov 4 12:06:18 2024 +0100

    Fix endless loop in lyx2lyx reversion routine
---
 lib/lyx2lyx/lyx_2_5.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/lyx2lyx/lyx_2_5.py b/lib/lyx2lyx/lyx_2_5.py
index d1730443af..4a1e5b1c27 100644
--- a/lib/lyx2lyx/lyx_2_5.py
+++ b/lib/lyx2lyx/lyx_2_5.py
@@ -1044,9 +1044,10 @@ def revert_mathml_version(document):
             # nothing to do
             break
 
-        # remove XHTML header if using the new value, leave alone otherwise.
+        # reset XHTML header if using the new value, leave alone otherwise.
         if "4" in document.header[i]:
             document.header[i] = "\\html_math_output 0"
+        break
 
     while True:
         i = find_token(document.header, "\\docbook_mathml_version", 0)