ESP32: fix bug in mkimage.sh

Fix the non-fatal `./build/mkimage.sh: line 38: [: =: unary operator
expected` error that can occur when no options are passed.

Signed-off-by: Winford <winford@object.stream>

Author: UncleGrumpy

CHANGELOG.md

@@ -9,6 +9,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 - Added Erlang distribution over serial (uart)
 
+### Fixed
+- Fixed bug in ESP32 mkimage.sh leading to non-fatal "unary operator expected" error
+
 ## [0.7.0-alpha.1] - 2026-04-06
 
 ### Added

src/platforms/esp32/tools/mkimage.sh.in

@@ -35,7 +35,9 @@ fail()
     exit 1
 }
 
-if [ "${@}" = "--help" ]; then
+opts="${@}"
+
+if [ "${opts}" = "--help" ]; then
     escript "@CMAKE_BINARY_DIR@/mkimage.erl" --help
     exit 0
 fi