[webkit] Fix the way to build curl when needed

Useful for tracking down networking issues.

Change-Id: I46a3a377deef65545b2ffebf015c679c4baef6e6
diff --git a/Tools/fuchsia/build_curl.sh b/Tools/fuchsia/build_curl.sh
index c78d5f7..d2938b1 100755
--- a/Tools/fuchsia/build_curl.sh
+++ b/Tools/fuchsia/build_curl.sh
@@ -44,7 +44,7 @@
   esac
 done
 
-if [ $clean_build = "false" ] || [ $just_make = "true" ]; then
+if [ $clean_build = "false" ] && [ $just_make = "false" ]; then
     has_stamp curl
 else
     __has_stamp=false