Changing EdgeThickness moves PanFrameRight.win to a wrong position

[ThomasAdam]

When changing EdgeThickness, e.g. from default (2) to 1, PanFrameRight.win is
reconfigured with the wrong position (lower right corner instead of upper
right corner). Moving to a page at the right of the current page with the
mouse does not work as expected after that.

Illustrated by xwininfo after starting with EdgeThickness=2 and then
changing to EdgeThickness=1.

The window in question is 0x200169.

goeran@DellLap1:~$ xwininfo -tree -root | head -30

xwininfo: Window id: 0x7a6 (the root window) (has no name)

Root window id: 0x7a6 (the root window) (has no name)
Parent window id: 0x0 (none)
53 children:
0x20016a (has no name): () 1920x2+0+1078 +0+1078
0x200167 (has no name): () 1920x2+0+0 +0+0
0x200169 (has no name): () 2x1080+1918+0 +1918+0
0x200168 (has no name): () 2x1080+0+0 +0+0
0x2001bf (has no name): () 101x16+0+0 +0+0
0x2000d8 "FVWM": ("fvwm" "FVWM") 10x10+-10+-10 +-10+-10

goeran@DellLap1:~$ xwininfo -tree -root | head -30

xwininfo: Window id: 0x7a6 (the root window) (has no name)

Root window id: 0x7a6 (the root window) (has no name)
Parent window id: 0x0 (none)
57 children:
0x200167 (has no name): () 1920x1+0+0 +0+0
0x200168 (has no name): () 1x1080+0+0 +0+0
0x200169 (has no name): () 1x1080+1919+1080 +1919+1080
0x20016a (has no name): () 1920x1+0+1079 +0+1079
0x200aa2 (has no name): () 61x51+1610+17 +1610+17
0x200a51 (has no name): () 129x205+1524+0 +1524+0
0x200950 (has no name): () 114x161+1650+207 +1650+207
0x2001bf (has no name): () 101x16+0+0 +0+0