tests/fate-run: do not attempt to parse tiny_psnrs output if it failed

This avoids confusing syntax errors with awk later

Likely fixes awk errors at:
http://buildd.debian-ports.org/status/fetch.php?pkg=ffmpeg&arch=sparc64&ver=7%3A2.6.2-1&stamp=1428928967Reviewed-by: Timothy Gu <timothygu99@gmail.com>
Thanks-to: Andreas Cadhalpun <andreas.cadhalpun@googlemail.com> for the link
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

tests/fate-run.sh

@@ -43,7 +43,7 @@ compare(){
 }
 
 do_tiny_psnr(){
-    psnr=$(tests/tiny_psnr "$1" "$2" $cmp_unit $cmp_shift 0)
+    psnr=$(tests/tiny_psnr "$1" "$2" $cmp_unit $cmp_shift 0) || return 1
     val=$(expr "$psnr" : ".*$3: *\([0-9.]*\)")
     size1=$(expr "$psnr" : '.*bytes: *\([0-9]*\)')
     size2=$(expr "$psnr" : '.*bytes:[ 0-9]*/ *\([0-9]*\)')