patch 8.2.0824: still not enough memory allocated when converting stringv8.2.0824

Problem:    Still not enough memory allocated when converting string with
            special character.
Solution:   Reserve space for expanding K_SPECIAL. (closes #6130)

1 files changed, 4 insertions, 3 deletions

diff --git a/src/eval.c b/src/eval.c
index d76ec94102..87b7644251 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -3515,10 +3515,11 @@ get_string_tv(char_u **arg, typval_T *rettv, int evaluate)
 	{
 	    ++p;
 	    // A "\<x>" form occupies at least 4 characters, and produces up
-	    // to 9 characters (6 for the char and 3 for a modifier): reserve
-	    // space for 5 extra.
+	    // to 21 characters (3 * 6 for the char and 3 for a modifier):
+	    // reserve space for 18 extra.
+	    // Each byte in the char could be encoded as K_SPECIAL K_EXTRA x.
 	    if (*p == '<')
-		extra += 5;
+		extra += 18;
 	}
     }