Fix crash on reading wrong function declaration DWARF.
* dwarf2read.c (read_subroutine_type): New variable void_type.
Pre-fill all TYPE_FIELD_TYPEs. Move nparams and iparams initialization
more close to their use.
gdb/testsuite/
* gdb.dwarf2/dw2-bad-parameter-type.exp,
gdb.dwarf2/dw2-bad-parameter-type.S: New.