Only compile regex portion of folder filter

The code was trying to compile the `~` as well. In this case, it was
trying to match a literal `~` to the front of the supplied regex.

Fixes: 334ca89bea ("folder filter: only assume regex if filter is
~fmt")

Signed-off-by: Daniel Xu <dxu@dxuuu.xyz>

widgets/dirlist.go

@@ -165,7 +165,7 @@ func folderMatches(folder string, pattern string) bool {
 		return false
 	}
 	if pattern[0] == '~' {
-		r, err := regexp.Compile(pattern)
+		r, err := regexp.Compile(pattern[1:])
 		if err != nil {
 			return false
 		}