misc: fix spellchecker

When codespell automatically fixes the spelling error, the "Fixed"
message seems goes to stderr. Check both the output and diffs should
make it more robust.

Also need quote output variables.

maint/hooks/spellchecker

@@ -45,9 +45,10 @@ do
     if [[ -f $file && $file != *.tex ]]; then
         cp -p ${file} ${TMP_FILENAME}
         output=$(bash maint/spellcheck.sh ${file})
-        git --no-pager diff ${file} ${TMP_FILENAME}
-        if [ -n "$output" ] ; then
-            echo $output
+        diffs=$(git --no-pager diff ${file} ${TMP_FILENAME})
+        if test -n "$output" -o -n "$diffs" ; then
+            echo "$output"
+            echo "$diffs"
             ret=1
         fi
     fi