Update 'mktemp' invocation

Turns out using "-t TEMPLATE" instead of "TEMPLATE" is causing TMPDIR to
override the setting from `-p`, which is the opposite of what the man
page says it does.

optipdf

@@ -42,12 +42,6 @@ KEEP_BACKUP_SUFFIX=
 FORCE_OVERWRITE=0
 ENCODE_THRU_WARNINGS=0
 
-TEMP_DIR=$(mktemp -d -t "${0##*/}.XXXXXX")
-cleanup() {
-    rm -fr -- "$TEMP_DIR"
-}
-trap 'cleanup' EXIT
-
 FILES=()
 NO_MORE_FLAGS=0
 for ARG; do
@@ -104,9 +98,11 @@ for ARG; do
     fi
 done
 
+TEMP_DIR=
+
 if [[ ${#FILES[@]} -eq 0 ]]; then
     USAGE >&2
-    exit 1
+    exit 2
 fi
 
 file_size() {
@@ -159,6 +155,16 @@ hr_size() (
     printf '%g %s\n' "$HR_VAL" "$HR_UNIT"
 )
 
+setup_tempdir() {
+    if [[ -z $TEMP_DIR ]]; then
+        TEMP_DIR=$(mktemp -d -t "${0##*/}.XXXXXX")
+        cleanup() {
+            rm -fr -- "$TEMP_DIR"
+        }
+        trap 'cleanup' EXIT
+    fi
+}
+
 # copies $2 over to $1 if $2 is smaller than $1
 use_smaller() {
     # if `$TEMP' isn't empty and it's of a smaller size than `$FILE',
@@ -250,7 +256,8 @@ fi
 ERRORS=0
 FREED_TOTAL=0
 for FILE in "${FILES[@]}"; do
-    TEMP=$(mktemp -p "$TEMP_DIR" -t 'file.XXXXXX')
+    setup_tempdir
+    TEMP=$(mktemp -p "$TEMP_DIR" 'file.XXXXXX')
     rm -f -- "$TEMP"
     BEGIN_FILESIZE=$(file_size "$FILE")