fix [#34745] TGA with size of 4Kx8K won't load

Checked the size limit on TGA files in svn history and this is was just an arbitrary limit that might have made sense some years back, but not now.


git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@55557 954f8c5b-7b00-dc11-b283-0030488c597c