hush: fix SEGV in % expansion

function                                             old     new   delta
expand_variables                                    2203    2217     +14

diff --git a/shell/hush_test/hush-vars/var_posix1.right b/shell/hush_test/hush-vars/var_posix1.right
index 47d52a6..e6cba27 100644
--- a/shell/hush_test/hush-vars/var_posix1.right
+++ b/shell/hush_test/hush-vars/var_posix1.right
@@ -32,4 +32,5 @@
 ababcdcd
 Empty:
 ababcdcd}_tail
+ababcdcd
 end
diff --git a/shell/hush_test/hush-vars/var_posix1.tests b/shell/hush_test/hush-vars/var_posix1.tests
index 3069360..c1f6409 100755
--- a/shell/hush_test/hush-vars/var_posix1.tests
+++ b/shell/hush_test/hush-vars/var_posix1.tests
@@ -43,5 +43,6 @@
 echo Empty:${var%%*}
 echo ${var#}}_tail
 # UNFIXED BUG: echo ${var#\}}_tail
+echo ${var%\\*}
 
 echo end