`PyUnstable_CopyPerfMapFile` calls fflush even when the file fails to open.

[AZero13]

Bug report

Bug description:

It should not be doing that. It should be checking first.

CPython versions tested on:

CPython main branch

Operating systems tested on:

macOS

Linked PRs

• gh-142571: Check for errors before calling each syscall in PyUnstable_CopyPerfMapFile() #142460
• [3.14] gh-142571: Check for errors before calling each syscall in PyUnstable_CopyPerfMapFile() (GH-142460) #142600
• [3.13] gh-142571: Check for errors before calling each syscall in PyUnstable_CopyPerfMapFile() (GH-142460) #142602