libext2fs: Add some fail-safe checks to the 32-bit bitmap code

libext2fs: Add some fail-safe checks to the 32-bit bitmap code

If a 64-bit bitmap is passed to a 32-bit bitmap function, add some
checks to make sure that we print a useful error message so we can
better catch potential problems.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>