#566 mged -Werror=maybe-uninitialized with gcc 10

[Reini Urban]

analog to #564

[100%] Linking C executable ../../bin/mged
brlcad/src/mged/edsol.c: In function ‘get_solid_keypoint.constprop’:
brlcad/src/mged/edsol.c:2506:5: error: ‘mpt[0]’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
2506 | MAT4X3PNT(pt, mat, mpt);
| ^
brlcad/src/mged/edsol.c:2506:5: error: ‘mpt[1]’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
brlcad/src/mged/edsol.c:2506:5: error: ‘mpt[2]’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
lto1: all warnings being treated as errors
make[3]: *** [/tmp/ccaOlIf0.mk:32: /tmp/mged.Lzg9w0.ltrans10.ltrans.o] Error 1