make: fix 'make monitor' target when core dump is not enabled

components/esptool_py/Makefile.projbuild

@@ -134,12 +134,13 @@ simple_monitor: $(call prereq_if_explicit,%flash) | check_python_dependencies
 
 PRINT_FILTER ?=
 
-MONITOR_CORE_DUMP_DECODE ?=
-ifdef CONFIG_ESP32_CORE_DUMP_DECODE
-MONITOR_CORE_DUMP_DECODE = --decode-coredumps $(CONFIG_ESP32_CORE_DUMP_DECODE)
+MONITOR_CORE_DUMP_DECODE_ARG ?=
+MONITOR_CORE_DUMP_DECODE = $(call dequote,$(CONFIG_ESP32_CORE_DUMP_DECODE))
+ifneq ("$(MONITOR_CORE_DUMP_DECODE)","")
+MONITOR_CORE_DUMP_DECODE_ARG = --decode-coredumps $(MONITOR_CORE_DUMP_DECODE)
 endif
 
-MONITOR_OPTS := --baud $(MONITORBAUD) --port $(ESPPORT) --toolchain-prefix $(CONFIG_SDK_TOOLPREFIX) --make "$(MAKE)" --print_filter "$(PRINT_FILTER)" $(MONITOR_CORE_DUMP_DECODE)
+MONITOR_OPTS := --baud $(MONITORBAUD) --port $(ESPPORT) --toolchain-prefix $(CONFIG_SDK_TOOLPREFIX) --make "$(MAKE)" --print_filter "$(PRINT_FILTER)" $(MONITOR_CORE_DUMP_DECODE_ARG)
 
 monitor: $(call prereq_if_explicit,%flash) | check_python_dependencies
 	$(summary) MONITOR