lib/vector/Vlib: Fix Resource Leak issue in break_polygons.c

[ShubhamDesai]

This pull request fixes issue identified by Coverity scan (CID: 1207832).
Changes Made:

• Each call to open(filename, O_RDWR | O_CREAT | O_EXCL, 0600) now checks if the file descriptor (fd or xpntfd) was successfully created.
• If file creation fails, G_fatal_error() is invoked, and the temporary filename is freed before the function exits.
• If xpntfd creation fails, it also cleans up by destroying the RTree and closing fd.
• Also there is a check for remove(filename). I have used G_warning over there to print message. Not sure whether to use G_fatal or G_warning.

[nilason]

Some suggestions.
And please address CID 1207831 too with this PR.

[ShubhamDesai]

Some suggestions. And please address CID 1207831 too with this PR.

Done

[nilason]

Thanks!