When running gdb v7.6 up to current HEAD (ee7e95efb9) with the mi2 interpreter, and trying to view disassembly in mode 4 (mixed source and disassembly), the line number argument is being ignored. 

for example
```
-file-exec-and-symbols /home/csmith/git/pygdbmi/pygdbmi/tests/sample_c_app/a.out
-data-disassemble -f /home/csmith/git/pygdbmi/pygdbmi/tests/sample_c_app/hello.c -l 16 -n 1 4\n
^done,asm_insns=[src_and_asm_line={line="16",file="hello.c",fullname="/home/csmith/git/pygdbmi/pygdbmi/tests/sample_c_app/hello.c",line_asm_insn=[{address="0x000000000040057d",func-name="main",offset="0",inst="push   %rbp"}]}]
```

but when I try to look at the next line (17), it outputs the same line (16):
```
-data-disassemble -f /home/csmith/git/pygdbmi/pygdbmi/tests/sample_c_app/hello.c -l 17 -n 1 4
^done,asm_insns=[src_and_asm_line={line="16",file="hello.c",fullname="/home/csmith/git/pygdbmi/pygdbmi/tests/sample_c_app/hello.c",line_asm_insn=[{address="0x000000000040057d",func-name="main",offset="0",inst="push   %rbp"}]}]
```