gst/multifile/gstmultifilesrc.*: When subsequent files are read, if the file doesn't exist, send an EOS instead of ca...

Original commit message from CVS:
* gst/multifile/gstmultifilesrc.c:
* gst/multifile/gstmultifilesrc.h:
When subsequent files are read, if the file doesn't exist, send
an EOS instead of causing an error.