tplink-safeloader: fix chunked support-list prints

tplink-safeloader: fix chunked support-list prints

When reading long support-list partitions, to print out as image info,
the string is read in chunks of 128 bytes. However, in cases where there
is more than one chunk, they are not properly terminated. This leads to
an out-of-bounds access by puts() printing the buffer chunks.

Ensure the read partial string is always NULL terminated, and print
chunk by chunk without extra line terminations. Terminate still with a
newline to maintain current behaviour.

Fixes: e1d76f4e8721 ("firmware-utils: tplink-safeloader: support displaying fw info")
Signed-off-by: Sander Vanheule <sander@svanheule.net>