modem-helpers: Don't leak strings when parsing DTMF response

`g_ptr_array_new()` creates an array without a free func,
this means we'd leak the strings when the reference count
drops to 0.

Fixes: 56fe8e7d3 ("modem-helpers: add utility function to split DTMF runs")

Signed-off-by: Guido Günther <agx@sigxcpu.org>

src/mm-base-call.c

@@ -766,7 +766,6 @@ static void
 send_dtmf_context_free (SendDtmfContext *ctx)
 {
     send_dtmf_context_clear_timeout (ctx);
-    g_ptr_array_foreach (ctx->dtmfs, (GFunc) g_free, NULL);
     g_ptr_array_free (ctx->dtmfs, TRUE);
     g_assert (!ctx->saved_error);
     g_slice_free (SendDtmfContext, ctx);

src/mm-modem-helpers.c

@@ -5895,7 +5895,7 @@ mm_dtmf_split (const gchar *dtmf)
     const gchar *p = dtmf;
     GString     *cur = NULL;
 
-    array = g_ptr_array_new ();
+    array = g_ptr_array_new_with_free_func (g_free);
 
     while (*p) {
         if (*p == MM_CALL_DTMF_PAUSE_CHAR) {