DRC fails wrongly with minimally-spaced pads at 45 degree angle.

Description

On a board with 0.2mm minimum clearance, 0.2mm wide pads at 0.4mm pitch fail DRC if the component is rotated 45 degrees.

Steps to reproduce

1. Create a new project with default settings (0.2mm clearance).
2. Insert two copies of nRF52832-QFxx from the MCU_Nordic library. The footprint has 0.2mm pads at 0.4mm pitch.
3. Place footprints on PCB.
4. Change the orientation of one footprint to 45 degrees.
5. Run DRC. The 45 degree part generates errors between every pair of adjacent pads. The other is OK.

KiCad Version

5.1.5+dfsg1-2 installed from Debian package.