Fix some issues reported by Coverity Scan (#846)

Fix some issues reported by Coverity Scan (#846)

* test_tile_decoder: Fix potential buffer overflow (coverity)

CID 1190155 (#1 of 1): Unbounded source buffer (STRING_SIZE)

Using a pointer instead of buffer of fixed size avoids the limit
for the length of the input file name.

Signed-off-by: Stefan Weil <sw@weilnetz.de>
* test_tile_encoder: Fix potential buffer overflow (coverity)

CID 1190154 (#1 of 1): Unbounded source buffer (STRING_SIZE)

Using a pointer instead of buffer of fixed size avoids the limit
for the length of the output file name. This implies that the length
can exceed 255, so the data type for variable len had to be fixed, too.

Signed-off-by: Stefan Weil <sw@weilnetz.de>
* openjpip: Initialize data before returning it

This fixes an error reported by Coverity:

CID 1190143 (#1 of 1): Uninitialized scalar variable (UNINIT)

Signed-off-by: Stefan Weil <sw@weilnetz.de>