Remove extension from lottie2ffmpeg and fix crash when lottieconverter not present

mautrix_telegram/util/lottie2ffmpeg

@@ -0,0 +1,26 @@
+#!/bin/bash
+TMPDIR=$(mktemp -d)
+
+if [ ! -e $TMPDIR ]; then
+    >&2 echo "Failed to create temp directory"
+    exit 1
+fi
+
+trap "exit 1"           HUP INT PIPE QUIT TERM
+trap 'rm -rf "$TMPDIR"' EXIT
+
+cd $TMPDIR
+
+lottieconverter=$1
+resolution=$2
+
+cat > input
+
+for i in {0..99}; do
+	padded="0$i"
+	$lottieconverter input frame-${padded: -2}.png png $resolution $((i+1))
+done
+
+ffmpeg -start_number 0 -framerate 30 -i frame-%02d.png -c:v libvpx-vp9 -pix_fmt yuva420p out.webm
+
+cat out.webm