The user can specify a custom soundfont to be used with fluidsynth.
There was previously a hack for the iOS7 backend to get the path to
the document folder where the user can put files in a sandboxed
environment. This hack was removed in commit:
cac0664757
The problem however occurred when creating a FSNode from the full
system path because FSNode uses makeFileNodePath, which already
prepends the root. So the full path is added twice which causes the
fileNode.exists() to fail.
Create the FSNode from the path to the soundfont and check if the
file exist. If so then return the full path.
Cherry-pick of: addbdc13c5
Git conflict manually fixed
f921c6acd9