Crash when trying to zoom on empty figure

[Jonathan Bieler]

When running this

using Immerse
figure()

And then clicking on the zoom icon I get:

julia> FATAL ERROR: Gtk state corrupted by error thrown in a callback:
ERROR: MethodError: `getindex` has no method matching getindex(::Void, ::Int64)
 in _aes at /Users/bieler/.julia/v0.4/Immerse/src/display_gadfly.jl:58
 in call at /Users/bieler/.julia/v0.4/Immerse/src/display_gadfly.jl:444
 in panzoom_cb at /Users/bieler/.julia/v0.4/Immerse/src/display_gadfly.jl:467
 in panzoom_wrapper at /Users/bieler/.julia/v0.4/Immerse/src/display_gadfly.jl:225
 in anonymous at /Users/bieler/.julia/v0.4/Gtk/src/events.jl:2
 in g_sigatom at /Users/bieler/.julia/v0.4/Gtk/src/GLib/signals.jl:168
 in gtk_main at /Users/bieler/.julia/v0.4/Gtk/src/events.jl:1

ERROR (unhandled task failure): MethodError: `getindex` has no method matching getindex(::Void, ::Int64)
 in _aes at /Users/bieler/.julia/v0.4/Immerse/src/display_gadfly.jl:58
 in call at /Users/bieler/.julia/v0.4/Immerse/src/display_gadfly.jl:444
 in panzoom_cb at /Users/bieler/.julia/v0.4/Immerse/src/display_gadfly.jl:467
 in panzoom_wrapper at /Users/bieler/.julia/v0.4/Immerse/src/display_gadfly.jl:225
 in anonymous at /Users/bieler/.julia/v0.4/Gtk/src/events.jl:2
 in g_sigatom at /Users/bieler/.julia/v0.4/Gtk/src/GLib/signals.jl:168
 in gtk_main at /Users/bieler/.julia/v0.4/Gtk/src/events.jl:1

I seems something is not initialized (or checked) correctly.

v0.4.1 on OS X