pdftoppm creates empty files when it runs out of space

[apyrgio]

We have seen that the pdftoppm tool can create empty files, if it cannot write in them due to lack of space (ENOSPC). Worse, it doesn't fail its execution, leading to a cryptic "Error converting PDF to Pixels (Invalid PPM header)" error, when our callback handler attempts to convert PPM files to RGB.

This is something we have seen as a side-effect of #574. This lack of reliability is worrisome, so it's probably best to see if we can use another tool.

[apyrgio]

Actually, this error is a duplicate of an error @deeplow had already reported: #524. Closing this error in favor of the older one.

[deeplow]

Looks like you forgot to close it