patch 8.1.1833: allocating a bit too much when there is no bad word.

Problem:    Allocating a bit too much when spellbadword() does not find a bad
            word.
Solution:   Reset "len" when going to the next word. (Daniel Hahler,
            closes #4788)
diff --git a/src/evalfunc.c b/src/evalfunc.c
index 07a6768..29857d3 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -10755,6 +10755,7 @@
 		}
 		str += len;
 		capcol -= len;
+		len = 0;
 	    }
 	}
     }