Added missing break in switch/case

That missing break is not just a memory leak:
It results in incorrect call to mdb_unicode2ascii for binary data!
I suspect that is what is causing segfault on some db as repported on
https://github.com/brianb/mdbtools/issues/19

src/libmdb/data.c

@@ -930,6 +930,7 @@ char *mdb_col_to_string(MdbHandle *mdb, void *buf, int start, int datatype, int
 				text = g_malloc(size);
 				memcpy((char*)buf+start, text, size);
 			}
+		break;
 		case MDB_TEXT:
 			if (size<0) {
 				text = g_strdup("");