wget: fix fname_out usage wrt redirects

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/networking/wget.c b/networking/wget.c
index 9d50437..bc92283 100644
--- a/networking/wget.c
+++ b/networking/wget.c
@@ -604,8 +604,14 @@
 		if (G.fname_out[0] == '/' || !G.fname_out[0])
 			G.fname_out = (char*)"index.html";
 		/* -P DIR is considered only if there was no -O FILE */
-		if (G.dir_prefix)
-			G.fname_out = fname_out_alloc = concat_path_file(G.dir_prefix, G.fname_out);
+		else {
+			if (G.dir_prefix)
+				G.fname_out = fname_out_alloc = concat_path_file(G.dir_prefix, G.fname_out);
+			else {
+				/* redirects may free target.path later, need to make a copy */
+				G.fname_out = fname_out_alloc = xstrdup(G.fname_out);
+			}
+		}
 	}
 #if ENABLE_FEATURE_WGET_STATUSBAR
 	G.curfile = bb_get_last_path_component_nostrip(G.fname_out);