_dbus_poll_select (): fix concating multiple verbose lines

11 jobs for misc-windows-fixes in 23 minutes and 30 seconds (queued for 9 seconds)
Status Job ID Name Coverage
  Build
passed #5758345
build:cmake

00:09:16

passed #5758342
build:debug

00:14:26

manual #5758347
allowed to fail manual
build:i686-w64-mingw32-cmake
passed #5758346
build:i686-w64-mingw32-debug

00:09:57

manual #5758344
allowed to fail manual
build:legacy
passed #5758341
build:production

00:10:13

manual #5758343
allowed to fail manual
build:reduced
manual #5758350
allowed to fail manual
build:stretch
passed #5758348
build:x86_64-w64-mingw32

00:08:33

passed #5758349
build:x86_64-w64-mingw32-cmake-debug

00:13:41

manual #5758351
allowed to fail manual
build:xenial