Incomplete micromanager acquisitions cause out of bounds error

[tlnagy]

Aborted micromanager acquisitions can cause BoundsErrors:

BoundsError: attempt to access 260-element Array{Union{Nothing, Tuple{String,String}},1} at index [261]

Stacktrace:
 [1] setindex! at ./array.jl:766 [inlined]
 [2] ifdindex!(::Array{Union{Nothing, NTuple{4,Int64}},1}, ::Array{Union{Nothing, Tuple{String,String}},1}, ::Set{String}, ::EzXML.Node, ::NamedTuple{(:Y, :X, :Z, :C, :T, :P),NTuple{6,Int64}}, ::String, ::Int64) at /home/tlnagy/.julia/dev/OMETIFF/src/parsing.jl:61
 [3] load(::Stream{DataFormat{:OMETIFF},IOStream}) at /home/tlnagy/.julia/dev/OMETIFF/src/loader.jl:51
 [4] (::getfield(Main, Symbol("##3#4")))(::IOStream) at ./In[6]:3
 [5] #open#312(::Base.Iterators.Pairs{Union{},Union{},Tuple{},NamedTuple{(),Tuple{}}}, ::typeof(open), ::getfield(Main, Symbol("##3#4")), ::String) at ./iostream.jl:375
 [6] open(::Function, ::String) at ./iostream.jl:373
 [7] top-level scope at In[6]:1

This appears to happen due to there being extra TiffData elements versus the dimensions reported by Pixels.