Assertion failure on current master

[Neil Puttock]

Hey guys,

I can't complete test-baseline due to an assertion error running
mozart-hrn-3.ly.  Here's the backtrace:

Drawing systems...lilypond: ../flower/include/interval.hh:226: T
Interval_t<T>::center() const [with T = double]: Assertion `!is_empty
()' failed.

Program received signal SIGABRT, Aborted.

(gdb) bt
#0  0x00007ffff508fd05 in raise (sig=6)
    at ../nptl/sysdeps/unix/sysv/linux/raise.c:64
#1  0x00007ffff5093ab6 in abort () at abort.c:92
#2  0x00007ffff50887c5 in __assert_fail (assertion=0x70bd60 "!is_empty ()",
    file=<value optimised out>, line=226, function=<value optimised out>)
    at assert.c:81
#3  0x000000000041bf01 in Interval_t<double>::center (this=0x7fffffff7310)
    at ../flower/include/interval.hh:226
#4  0x00000000006d8b2c in Tuplet_number::calc_y_offset (smob=0x7ffff22bebe0)
    at tuplet-number.cc:83
#5  0x00007ffff7926ae4 in scm_dapply () from /usr/lib/libguile.so.17
#6  0x00000000004fc65f in Grob::try_callback_on_alist (this=0x108d150,
    alist=0x108d1b0, sym=0x7ffff2a6c080, proc=0x7ffff45ac530)
    at grob-property.cc:231
#7  0x00000000004fc398 in Grob::internal_get_property (this=0x108d150,
    sym=0x7ffff2a6c080) at grob-property.cc:188
#8  0x0000000000505efd in Grob::get_offset (this=0x108d150, a=Y_AXIS)
    at grob.cc:383
#9  0x0000000000505a67 in Grob::relative_coordinate (this=0x108d150,
    refp=0x184dc00, a=Y_AXIS) at grob.cc:312
#10 0x00000000005062a4 in Grob::extent (this=0x108d150, refp=0x184dc00,
    a=Y_AXIS) at grob.cc:427
#11 0x000000000043a1ad in add_boxes (me=0x108d150, x_common=0x18950a0,

Looks like the new tuplet collision avoidance code.

Cheers,
Neil