patch 9.0.0052: "zG" may throw an error if invalid character follows

Problem:    "zG" may throw an error if invalid character follows.
Solution:   Pass the word length to valid_spell_word(). (Ken Takata,
            closes #10737)
diff --git a/src/version.c b/src/version.c
index a6a80b6..3c4e96c 100644
--- a/src/version.c
+++ b/src/version.c
@@ -736,6 +736,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    52,
+/**/
     51,
 /**/
     50,