btp_parse_kerneloops() causes SIGSEGV if call trace is empty

[jfilak]

$ cat backtrace
irq 19: nobody cared (try booting with the "irqpoll" option)
Pid: 1, comm: systemd Not tainted 3.8.3-203.fc18.i686 #1
Call Trace:

$ abrt-action-generate-core-backtrace
Segmentation fault (core dumped)

$ gdb abrt-action-generate-core-backtrace
Thread 1 (Thread 0x7ffff7fcb7c0 (LWP 16986)):
#0 btp_parse_kerneloops (text=text@entry=0x607940 "irq 19: nobody cared (try booting with the "irqpoll" option)\nPid: 1, comm: systemd Not tainted 3.8.3-203.fc18.i686 #1\nCall Trace:\n",

kernelver=kernelver@entry=0x6079e0 "3.8.3-203.fc18.i686") at core-backtrace-oops.c:253
    result = <optimized out>
    nextline = <optimized out>
    line = <optimized out>
    ip = <optimized out>
    first = 0x0
    last = 0x0
    first_frame = <optimized out>
    last_frame = <optimized out>

#1 0x000000000040145b in main (argc=1, argv=) at abrt-action-generate-core-backtrace.c:197

    space = <optimized out>
    dump_dir_name = 0x401957 "."
    program_usage_string = <optimized out>
    program_options = {{type = OPTION_BOOL, short_name = 118, long_name = 0x40195c "verbose", value = 0x602160, argh = 0x0, help = 0x401959 "Be verbose"}, {type = OPTION_STRING, short_name = 100, long_name = 
0x0, value = 0x7fffffffdaf8, argh = 0x401964 "DIR", help = 0x401968 "Problem directory"}, {type = OPTION_BOOL, short_name = 114, long_name = 0x40197a "raw", value = 0x602168, argh = 0x0, help = 
0x40197e "Do not hash fingerprints"}, {type = OPTION_END, short_name = 0, long_name = 0x0, value = 0x0, argh = 0x0, help = 0x0}}
    dd = 0x607390
    analyzer = <optimized out>
    executable = 0x6073c0 ""
    txt_backtrace = 0x607940 "irq 19: nobody cared (try booting with the \"irqpoll\" option)\nPid: 1, comm: systemd Not tainted 3.8.3-203.fc18.i686 #1\nCall Trace:\n"
    kernel = 0x6079e0 "3.8.3-203.fc18.i686"
    backtrace = <optimized out>
    formatted_backtrace = <optimized out>