scripts/qemu-version.sh: Add missing space before ']'

When configure has been run with --with-pkgversion=xyz, the shell complains
about a missing ']' in this script.

Fixes: 2c273f32d3 ("meson: generate qemu-version.h")
Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

scripts/qemu-version.sh

@@ -6,7 +6,7 @@ dir="$1"
 pkgversion="$2"
 version="$3"
 
-if [ -z "$pkgversion"]; then
+if [ -z "$pkgversion" ]; then
     cd "$dir"
     if [ -e .git ]; then
         pkgversion=$(git describe --match 'v*' --dirty | echo "")