newapkbuild: fix empty function regression

Since the obsolete 'cd "$builddir"' statements have been removed in [1],
build(), check() and package() can generate empty functions if no build
system is specified or if there is no default for the given build
system. newapkbuild will then fail, as it tries to parse the script it
generated:

$ cd /home/pmos && newapkbuild test
/usr/bin/abuild: /home/pmos/test/APKBUILD: line 18: syntax error: unexpected "}"
$ cat test/APKBUILD
...
build() {
}
...

Fix this by placing ":" in functions that would be empty.

[1]: f83d19ce79ab9f2dcc5238346a910cd18ae0f330

newapkbuild.in

@@ -104,6 +104,13 @@ build_python() {
 __EOF__
 }
 
+build_empty() {
+	cat >>APKBUILD<<__EOF__
+	# Replace with proper build command(s)
+	:
+__EOF__
+}
+
 check_make() {
 	cat >>APKBUILD<<__EOF__
 	make check
@@ -116,6 +123,13 @@ check_python() {
 __EOF__
 }
 
+check_empty() {
+	cat >>APKBUILD<<__EOF__
+	# Replace with proper check command(s)
+	:
+__EOF__
+}
+
 # Package sections
 package_make() {
 	cat >>APKBUILD<<__EOF__
@@ -146,6 +160,13 @@ package_python() {
 __EOF__
 }
 
+package_empty() {
+	cat >>APKBUILD<<__EOF__
+	# Replace with proper package command(s)
+	:
+__EOF__
+}
+
 # Create new aport from templates
 newaport() {
 	local newname="${1##*/}"
@@ -281,6 +302,8 @@ __EOF__
 		build_perl;;
 	python)
 		build_python;;
+	*)
+		build_empty;;
 	esac
 
 	cat >>APKBUILD<<__EOF__
@@ -298,6 +321,8 @@ __EOF__
 		check_make;;
 	python)
 		check_python;;
+	*)
+		check_empty;;
 	esac
 
 	cat >>APKBUILD<<__EOF__
@@ -321,6 +346,8 @@ __EOF__
 		package_perl;;
 	python)
 		package_python;;
+	*)
+		package_empty;;
 	esac
 
 	if [ -n "$cpinitd" ]; then