Fixed mp_begin_iteration (H.Hagen)

[[Split portion of a mixed commit.]]

source/texk/web2c/luatexdir/ChangeLog

+2022-05-23  Luigi Scarso <luigi.scarso@gmail.com>
+    * Fixed mp_begin_iteration (H.Hagen)
+
 2022-05-15  Luigi Scarso <luigi.scarso@gmail.com>
     * Fixed a memory leak in mplib (H.Hagen)
 

source/texk/web2c/luatexdir/luatex_svnversion.h

 #ifndef luatex_svn_revision_h
 #define luatex_svn_revision_h
-#define luatex_svn_revision 7526
+#define luatex_svn_revision 7527
 #endif

source/texk/web2c/mplibdir/mp.w

@@ -21169,7 +21169,7 @@ void mp_begin_iteration (MP mp) {
       p->value_mod = mp_suffix_sym;
     }
     mp_get_x_next (mp);
-    if (cur_cmd() == mp_within_token) {
+    if (p->value_mod = mp_expr_sym && cur_cmd() == mp_within_token) {
       @<Set up a picture iteration@>;
     } else {
       @<Check for the assignment in a loop header@>;