solderpaste: Ensure there is a soldermask aperture onder paste

A lot of components do not clear the soldermask under the solderpaste.
This was noticed on first on
WQFN-24-1EP_4x4mm_P0.5mm_EP2.45x2.45mm_ThermalVias.kicad_mod, where a
square copper is layed out, and four dabs of solder paste are added,
without removing the soldermask on that layer.

According to KiBot warning W045, this is incorrect, and it kind-of makes
sense. We shouldn't apply solderpaste ontop of the soldermask. Granted,
one can argue that there should always be copper underneath solderpaste,
but right now, all 'dabs' of solderpaste are on an 'SMD Aparture', which
is indicated by not having (or double quoted) pad names. That would be
too big of a change and not scriptable anyway. Also, the paste 'dabs'
are not pads in the end.

The change was performed using sed and zsh, which supports the double
glob.

sed -i -e 's|(.pad "" smd .(layers) (F.Paste).)|\1 F.Mask \2|' **/.kicad_mod