`http_get_aria2c` should return proper value on `aria2c` failures

plugins/python-build/bin/python-build

@@ -341,8 +341,11 @@ http_head_aria2c() {
 
 http_get_aria2c() {
   local out="${2:-$(mktemp "out.XXXXXX")}"
-  aria2c --allow-overwrite=true -o "${out}" ${ARIA2_OPTS} "$1" >&4
-  [ -n "$2" ] || cat "${out}"
+  if aria2c --allow-overwrite=true -o "${out}" ${ARIA2_OPTS} "$1" >&4; then
+    [ -n "$2" ] || cat "${out}"
+  else
+    false
+  fi
 }
 
 http_head_curl() {