httpcaddyfile: Fix ordering of catch-all site blocks

Catch-alls should always go last. Normally this is the case, but we have
a special case for comparing one wildcard-host site block to another
non-wildcard host site block; and a catch-all site block is also a
non-wildcard host site block, so now we have to special-case the
catch-all site block. Sigh.

This could be reproduced with a Caddyfile that has two site blocks:
":80" and "*.example.com", in that order.

caddyconfig/httpcaddyfile/httptype.go

@@ -400,6 +400,11 @@ func (st *ServerType) serversFromPairings(
 					jLongestPath = addr.Path
 				}
 			}
+			if specificity(jLongestHost) == 0 {
+				// catch-all blocks (blocks with no hostname) should always go
+				// last, even after blocks with wildcard hosts
+				return true
+			}
 			if iWildcardHost != jWildcardHost {
 				// site blocks that have a key with a wildcard in the hostname
 				// must always be less specific than blocks without one; see