Fix a potential problem that may read uninitialized memory region on a stack.

This problem was warned by gcc 4.8.1 on Ubuntu 13.10 as below.

cut-elf-loader.c: In function 'cut_elf_loader_is_elf':
cut-elf-loader.c:191:37: warning: 'ident[3]' may be used uninitialized in this function [-Wmaybe-uninitialized]
         (ident[EI_MAG2] == ELFMAG2) &&
                                     ^
cut-elf-loader.c:190:37: warning: 'ident[2]' may be used uninitialized in this function [-Wmaybe-uninitialized]
         (ident[EI_MAG1] == ELFMAG1) &&
                                     ^
cut-elf-loader.c:189:37: warning: 'ident[1]' may be used uninitialized in this function [-Wmaybe-uninitialized]
     if ((ident[EI_MAG0] == ELFMAG0) &&
                                     ^
cut-elf-loader.c:189:8: warning: 'ident[0]' may be used uninitialized in this function [-Wmaybe-uninitialized]
     if ((ident[EI_MAG0] == ELFMAG0) &&