[gimp-help] Fix validate_po to not show an error for <? ... ?> XML constructs

[Jacob Boerema <jboerema src gnome org>]

commit 7e4646ce764702768c4166d36e96e8532ff0a1cf
Author: Jacob Boerema <jgboerema gmail com>
Date:   Mon Jun 13 12:55:02 2022 -0400

    Fix validate_po to not show an error for <? ... ?> XML constructs
    
    (cherry picked from commit ae0f1f2a31ae2acd262c1744eb656dbe95cd9587)

 tools/test/test.po   | 7 ++++++-
 tools/validate_po.py | 6 ++++++
 2 files changed, 12 insertions(+), 1 deletion(-)
---
diff --git a/tools/test/test.po b/tools/test/test.po
index 89889681b..55a85c27b 100644
--- a/tools/test/test.po
+++ b/tools/test/test.po
@@ -107,7 +107,7 @@ msgstr ""
 "</emphasis>"
 
 #: src/menus/colors/desaturate/desaturate.xml:200(para)
-# ERROR: illegal vertical tab
+# ERROR: illegal vertical tab (currently a WARNING due to polib limitations)
 msgid ""
 "Using escaped\ttext\vnextline\n\"quote\" literal \\ etc."
 msgstr ""
@@ -155,3 +155,8 @@ msgstr ""
 "keycombo>). Εάν χρειάζεστε περισσότερη βοήθεια για το πώς να το κάνετε αυτό, "
 "ανατρέξτε στις <link linkend=\"anchor-floating-selection\">Αιωρούμενες "
 "επιλογές</link>."
+
+#: src/gimp.xml:29(year)
+#: OK: <? ... ?> defines commands in XML
+msgid "2002-<?dbtimestamp format=\"Y\"?>"
+msgstr "2002-<?dbtimestamp format=\"Y\"?>"
diff --git a/tools/validate_po.py b/tools/validate_po.py
index 8d8b48d61..e5245708f 100644
--- a/tools/validate_po.py
+++ b/tools/validate_po.py
@@ -88,6 +88,12 @@ class Validate(object):
                         print(f"WARNING: XML comment closing tag missing", file=self.log)
                     start_tag = -1
                     continue
+            elif end_tag > 2 and textblock[0] == '?' and textblock[end_tag-1] == '?':
+                # XML "external command"
+                # This can be improved to explicitly search for end with '?>'
+                textblock = textblock[end_tag+1:]
+                start_tag = textblock.find('<')
+                continue
 
             if end_tag > -1:
                 # Found left and right brackets: grab tag