aportgen: fix extra newline (!1811)

pmb/aportgen/core.py

@@ -91,10 +91,12 @@ def rewrite(args, pkgname, path_original, fields={}, replace_pkgname=None,
         "# Based on: " + path_original + "\n",
         "\n",
     ]
-    for line in below_header.split("\n"):
-        if not line[:8].strip():
-            line = line[8:]
-        lines_new += line.rstrip() + "\n"
+
+    if below_header:
+        for line in below_header.split("\n"):
+            if not line[:8].strip():
+                line = line[8:]
+            lines_new += line.rstrip() + "\n"
 
     # Copy/modify lines, skip Maintainer/Contributor
     path = args.work + "/aportgen/APKBUILD"

test/testdata/aportgen/pmaports/cross/binutils-armhf/APKBUILD

@@ -2,7 +2,6 @@
 # Generator: pmbootstrap aportgen binutils-armhf
 # Based on: main/binutils
 
-
 pkgname="binutils-armhf"
 pkgver=2.31.1
 pkgrel=1