make clean: invoke docker only when there is something to clean

examples/esp32/device-dashboard/Makefile

@@ -35,4 +35,4 @@ flash3:
 	cd build && $(ESPTOOL) --chip esp32 -p $(PORT) -b 460800 --before=default_reset --after=hard_reset write_flash --flash_mode dio --flash_freq 40m --flash_size 2MB 0x8000 partition_table/partition-table.bin 0x1000 bootloader/bootloader.bin 0x100000 mongoose-esp32-example.bin
 
 clean:
-	$(DOCKER) rm -rf build sdkconfig
+	test -d build && $(DOCKER) rm -rf build sdkconfig || true

examples/esp8266/http-client-server/Makefile

@@ -41,5 +41,5 @@ monitor: build
 .PHONY: build
 
 clean:
-	$(DOCKER) rm -rf src/build
+	test -d src/build && $(DOCKER) rm -rf src/build || true
 

examples/ti/ti-ek-tm4c1294xl-http-server/Makefile

@@ -9,7 +9,7 @@ build: | $(NAME)
 	$(DOCKER) /opt/ti/ccs/eclipse/eclipse -noSplash -data /workspace -application com.ti.ccstudio.apps.projectBuild -ccs.autoImport -ccs.projects $(NAME) -ccs.configuration Release
 
 clean:
-	$(DOCKER) rm -rf /workspace/$(NAME)
+	test -d $(NAME) && $(DOCKER) rm -rf /workspace/$(NAME) || true
 
 flash:	DOCKER_ARGS = -it --privileged -v /dev/bus/usb/:/dev/bus/usb -w /workspace
 flash: