Disclosure of uninitialized memory in stbi__tga_load in stb_image

stb_image is a single file MIT licensed library for processing images. The stbi__getn function reads a specified number of bytes from context (typically a file) into the specified buffer. In case the file stream points to the end, it returns zero. There are two places where its return value is not checked: In the `stbi__hdr_load` function and in the `stbi__tga_load` function. The latter of the two is likely more exploitable as an attacker may also control the size of an uninitialized buffer.