selection: unbreak text/uri-list decoding: we’re not using \r, not \n

Before passing the pasted text to the decoder, we now replace \r\n,
and \n, with \r.

The URI decoder was looking for a \n, which meant we failed to split
up the list and instead pasted a single “multi-line” URI.

selection.c

@@ -1254,7 +1254,7 @@ fdm_receive_decoder_uri(struct clipboard_receive *ctx, char *data, size_t size)
     char *start = ctx->buf.data;
     char *end = NULL;
 
-    while ((end = memchr(start, '\n', ctx->buf.idx - (start - ctx->buf.data))) != NULL) {
+    while ((end = memchr(start, '\r', ctx->buf.idx - (start - ctx->buf.data))) != NULL) {
         decode_one_uri(ctx, start, end - start);
         start = end + 1;
     }