[clang][analyzer] No end-of-file when seek to file begin.

If `fseek` is used with 0 position and SEEK_SET it sets the position
to the start of the file. This should not cause FEOF (end of file) error.
The case of an empty file is not handled for simplification.
It is not exactly defined in what cases `fseek` produces the different
error states. Normally feof should not happen at all because it is
possible to set the position after the end of file, but previous tests
showed that still feof (and any other error cases) can happen.

Reviewed By: donat.nagy

Differential Revision: https://reviews.llvm.org/D153363