MIPS16/GAS: Reject instructions that end with a dot

MIPS16/GAS: Reject instructions that end with a dot

Fix a regression from commit 3fb49709438e ("MIPS16/GAS: Fix forced size
suffixes with argumentless instructions") and reject MIPS16 instructions
that end with a dot and no forced size suffix following, e.g.:

$ cat test.s
	.set	mips16
foo:
	break.
	entry.
	addiu.	$2, 0x7fff
	addiu.	$3, $2, 0
	.align	8, 0
$ as -32 -o test.o test.s
$ objdump -d test.o

test.o:     file format elf32-tradbigmips

Disassembly of section .text:

00000000 <foo>:
   0:	e805      	break
   2:	e809      	entry
   4:	f7ef 4a1f 	addiu	v0,32767
   8:	4260      	addiu	v1,v0,0
	...
$

Add a test accordingly, also verifying invalid forced size suffixes.