support/download: properly catch missing hashes

When checking hashes reports no hash for a file, and this is treated as
an error (now: because BR2_ENFORCE_CHECK_HASH is set; later: because
that will be the new and only behaviour), exit promptly in error.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Arnout Vandecappelle <arnout@mind.be>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Reviewed-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

support/download/dl-wrapper

@@ -45,10 +45,19 @@ main() {
         error "no output specified, use -o\n"
     fi
 
-    # If the output file already exists, do not download it again
+    # If the output file already exists and:
+    # - there's no .hash file: do not download it again and exit promptly
+    # - matches all its hashes: do not download it again and exit promptly
+    # - fails at least one of its hashes: force a re-download
+    # - there's no hash (but a .hash file): consider it a hard error
     if [ -e "${output}" ]; then
         if support/download/check-hash ${quiet} "${hfile}" "${output}" "${output##*/}"; then
             exit 0
+        elif [ ${?} -ne 2 ]; then
+            # Do not remove the file, otherwise it might get re-downloaded
+            # from a later location (i.e. primary -> upstream -> mirror).
+            # Do not print a message, check-hash already did.
+            exit 1
         fi
         rm -f "${output}"
         warn "Re-downloading '%s'...\n" "${output##*/}"