Crash when deleting the gradient node and clicking the gradient line

Migrated from: https://bugs.launchpad.net/inkscape/+bug/1287989

Steps to reproduce:

• open Inkscape
• Draw a gradient on it
• Open the xml editor
• Open the <svg:defs... node
• Select the first <svg:linearGradient... node
• Press the Delete node button (top middle)
• With the gradient tool still active, double click on the gradient line

What happened?

Crash: bt-r13012.txt (from Launchpad), inkscape_backtrace.txt (current master)

What should have happened?

No crash.

Inkscape Version and Operating System:

• Inkscape Version: 1.1-dev (c990a67, 2020-04-09)
• Operating System: Windows 10
• Operating System version: 10.0.18362

inkscape_backtrace.txt