warning fix: add self-consitency check to remove warning

verify promise of code that more code can be pasted with an
assert at the end condition of the code passage that builds
string.

Change-Id: I76a4e5f91b9142fff932e1493cb43c29eb6a0f80
Signed-off-by: Øyvind Harboe <oyvind.harboe@zylin.com>
Reviewed-on: http://openocd.zylin.com/143
Tested-by: jenkins
Reviewed-by: Øyvind Harboe <oyvindharboe@gmail.com>

src/rtos/rtos.c

@@ -198,6 +198,9 @@ int gdb_thread_packet(struct connection *connection, char *packet, int packet_si
 				tmp_str_ptr += sprintf( tmp_str_ptr, " : %s", detail->extra_info_str );
 			}
 
+			assert(strlen(tmp_str) ==
+				(size_t) (tmp_str_ptr - tmp_str));
+
 			char * hex_str = (char*) malloc( strlen(tmp_str)*2 +1 );
 			str_to_hex( hex_str, tmp_str );