Valgrind: fix "definitely lost" memory from get_random_string() - test-vendor

==88804== 8 bytes in 1 blocks are definitely lost in loss record 12 of 479
==88804==    at 0x4848A13: calloc (in /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so)
==88804==    by 0x503C550: g_malloc0 (in /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0.7600.1)
==88804==    by 0x10B5D8: get_random_string_without (test-stuff.c:312)
==88804==    by 0x10B655: get_random_string (test-stuff.c:333)
==88804==    by 0x10AA92: test_string_fcn (test-vendor.c:138)
==88804==    by 0x10A76B: test_vendor (test-vendor.c:88)
==88804==    by 0x10AD5A: main (test-vendor.c:246)

+ 3 more

libgnucash/engine/test/test-vendor.c

@@ -117,13 +117,13 @@ test_vendor (void)
         g_list_free (list);
     }
     {
-        const char *str = get_random_string();
-        const char *res;
+        char *str = get_random_string();
 
         gncVendorSetName (vendor, str);
-        res = qof_object_printable (GNC_ID_VENDOR, vendor);
+        const char *res = qof_object_printable (GNC_ID_VENDOR, vendor);
         do_test (res != NULL, "Printable NULL?");
         do_test (g_strcmp0 (str, res) == 0, "Printable equals");
+        g_free (str);
     }
 
     qof_book_destroy (book);
@@ -135,7 +135,7 @@ test_string_fcn (QofBook *book, const char *message,
                  const char * (*get)(const GncVendor *))
 {
     GncVendor *vendor = gncVendorCreate (book);
-    char const *str = get_random_string ();
+    char *str = get_random_string ();
 
     do_test (!gncVendorIsDirty (vendor), "test if start dirty");
     gncVendorBeginEdit (vendor);
@@ -150,6 +150,7 @@ test_string_fcn (QofBook *book, const char *message,
      */
     // do_test (!gncVendorIsDirty (vendor), "test dirty after commit");
     do_test (g_strcmp0 (get (vendor), str) == 0, message);
+    g_free (str);
     gncVendorSetActive (vendor, FALSE);
     count++;
 }