meson: only add empty lines betwen active summary sections

Signed-off-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-by: Dylan Baker <dylan@pnwbakers.com>
10 jobs for !1176 with meson-summary-fixes in 7 seconds (queued for 1 second)
detached
Status Job ID Name Coverage
  Containers Build
canceled debian #388234

00:00:07

 
  Build+Test
skipped meson-clang #388236
skipped meson-clover #388240
skipped meson-main #388239
skipped meson-swr-glvnd #388235
skipped meson-vulkan #388241
skipped scons-llvm #388243
skipped scons-nollvm #388242
skipped scons-swr #388237
skipped scons-win64 #388238