Handle multiline responses to dbus-launch

Users may not have dbus properly configured, and their machine may respond
to dbus-launch with a multiline string that prints a warning before returning
the expected output. The code handling this response assumed that it would
always find '=' before it finds '\n', but this not true in the case of a
multiline string. Rather, it is the other way around, and thus the code sliced
the response with a lower bound greater than its upper bound, leading to a
"panic: runtime error: slice bounds out of range" crash.

Fixes #151
2 files changed