Ensure SOONG_CONV_DATA is generated even no modules require conversion

This change ensures that the `SOONG_CONV_DATA` file is always
generated, even when there are no modules that require conversion from
Make to Soong.
Previously, if no Android.mk files were present in the source code, the
`SOONG_CONV` variable would be empty, preventing the creation of
`SOONG_CONV_DATA` and causing build failures.

Bug: 382385324
Test: m $ANDROID_PRODUCT_OUT/obj/PACKAGING/soong_conversion_intermediates/soong_conv_data
Change-Id: Ifd9ec50e1615765f0d440a767a35f87d31a251f0

core/Makefile

diff --git a/core/Makefile b/core/Makefile
index 642c5bf..45561af 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -872,6 +872,7 @@
 SOONG_CONV_DATA := $(call intermediates-dir-for,PACKAGING,soong_conversion)/soong_conv_data
 $(SOONG_CONV_DATA):
 	@rm -f $@
+	@touch $@ # This file must be present even if SOONG_CONV is empty.
 	@$(foreach s,$(SOONG_CONV),echo "$(s),$(SOONG_CONV.$(s).TYPE),$(sort $(SOONG_CONV.$(s).PROBLEMS)),$(sort $(filter-out $(SOONG_ALREADY_CONV),$(SOONG_CONV.$(s).DEPS))),$(sort $(SOONG_CONV.$(s).MAKEFILES)),$(sort $(SOONG_CONV.$(s).INSTALLED))" >>$@;)
 
 $(call declare-1p-target,$(SOONG_CONV_DATA),build)