patch 8.1.1878: negative float before method not parsed correctly

Problem:    Negative float before method not parsed correctly.
Solution:   Apply "!" and "-" in front of expression before using ->.

src/version.c

@@ -769,6 +769,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1878,
 /**/
     1877,
 /**/