mverify: use 0+x to force number

+x does not work in nawk/*BSD awk.

contrib/mverify

@@ -8,9 +8,9 @@
 mshow -t "$1" | awk -v "msg=$1" '
 { match($0, "^ *"); indent = RLENGTH }
 $2 == "text/plain" { plain++ }
-$2 == "multipart/signed" { signed = +$1; si = indent; next }
-signed && !content && indent == si+2 { content = +$1; next }
-signed && content && !signature && indent == si+2 { signature = +$1; type = $2 }
+$2 == "multipart/signed" { signed = 0+$1; si = indent; next }
+signed && !content && indent == si+2 { content = 0+$1; next }
+signed && content && !signature && indent == si+2 { signature = 0+$1; type = $2 }
 function q(a) { gsub("\\47", "\47\\\47\47", a); return "\47"a"\47" }
 END {
 	if (type == "" && plain) {  // guess plain text armored signature