patch 8.1.0231: :help -? goes to help for -+

Problem:    :help -? goes to help for -+.
Solution:   Add -? to list of special cases. (Hirohito Higashi)
diff --git a/src/ex_cmds.c b/src/ex_cmds.c
index a30178b..3733151 100644
--- a/src/ex_cmds.c
+++ b/src/ex_cmds.c
@@ -6583,7 +6583,7 @@
     static char *(mtable[]) = {"*", "g*", "[*", "]*", ":*",
 			       "/*", "/\\*", "\"*", "**",
 			       "cpo-*", "/\\(\\)", "/\\%(\\)",
-			       "?", ":?", "?<CR>", "g?", "g?g?", "g??",
+			       "?", ":?", "-?", "?<CR>", "g?", "g?g?", "g??",
 			       "/\\?", "/\\z(\\)", "\\=", ":s\\=",
 			       "[count]", "[quotex]",
 			       "[range]", ":[range]",
@@ -6593,7 +6593,7 @@
     static char *(rtable[]) = {"star", "gstar", "[star", "]star", ":star",
 			       "/star", "/\\\\star", "quotestar", "starstar",
 			       "cpo-star", "/\\\\(\\\\)", "/\\\\%(\\\\)",
-			       "?", ":?", "?<CR>", "g?", "g?g?", "g??",
+			       "?", ":?", "-?", "?<CR>", "g?", "g?g?", "g??",
 			       "/\\\\?", "/\\\\z(\\\\)", "\\\\=", ":s\\\\=",
 			       "\\[count]", "\\[quotex]",
 			       "\\[range]", ":\\[range]",