[MCH, MID] small changes in handling empty TF

[pillot]

Hi @sawenzel ,
This is a follow up on #15705 and #15714.

• If there is no collision, we can as well skip entirely the noise-only digit generation to save time and send empty containers.
• I think a protection was missing in the MCH and MID digit readers when using IR frames.
  Cheers,
  Philippe

[alibuild]

Error while checking build/O2/fullCI_slc9 for 438a57a at 2026-09-08 17:07:

## sw/BUILD/O2-sim-challenge-test-latest/log
./sim-challenge.log[ERROR] SHUTTING DOWN DUE TO SIGNALED EXIT IN COMPONENT 209
./sim.log[ERROR] SHUTTING DOWN DUE TO SIGNALED EXIT IN COMPONENT 209


## sw/BUILD/o2checkcode-latest/log
--
========== List of errors found ==========
++ GRERR=0
++ grep -v clang-diagnostic-error error-log.txt
++ grep ' error:'
++ GRERR=1
++ [[ 1 == 0 ]]
++ mkdir -p /sw/INSTALLROOT/4f394abf75c9c023ec33dd9707526410d50fdbe7/slc9_x86-64/o2checkcode/1.0-local4/etc/modulefiles
++ alibuild-generate-module
+ HAS_BIN=
+ HAS_LIB=
+ HAS_CMAKE=
+ HAS_ROOT=
+ '[' 0 '!=' 0 ']'
+ cat
+ printf 'if ![ is-loaded '\''BASE/1.0'\'' ] {\n module load BASE/1.0\n}'
+ echo 'BUILD_REQUIRES=CMake alibuild-recipe-tools defaults-release'
BUILD_REQUIRES=CMake alibuild-recipe-tools defaults-release
+ FULL_BUILD_REQUIRES='bz2 FairCMakeModules defaults-release ninja safe_int date O2-customization CMake alibuild-recipe-tools double-conversion googlebenchmark UUID Alice-GRID-Utils MPFR json-c ninja-fortran pytorch_cpuinfo Python-modules-list'
+ echo 'FULL_BUILD_REQUIRES=bz2 FairCMakeModules defaults-release ninja safe_int date O2-customization CMake alibuild-recipe-tools double-conversion googlebenchmark UUID Alice-GRID-Utils MPFR json-c ninja-fortran pytorch_cpuinfo Python-modules-list'
FULL_BUILD_REQUIRES=bz2 FairCMakeModules defaults-release ninja safe_int date O2-customization CMake alibuild-recipe-tools double-conversion googlebenchmark UUID Alice-GRID-Utils MPFR json-c ninja-fortran pytorch_cpuinfo Python-modules-list
++ env
++ cut -f1 -d=
++ grep -v '^DEFAULT_'
++ grep -v PKGREVISION
++ grep -v ALIBUILD_RECIPE_TOOLS
++ grep REVISION
++ sed -e s/_REVISION//
+ for x in $(env | cut -f1 -d= | grep -v "^DEFAULT_" | grep -v PKGREVISION | grep -v ALIBUILD_RECIPE_TOOLS | grep REVISION | sed -e 's/_REVISION//')
++ eval 'echo $LIBFFI_REVISION'
+++ echo 14
+ REVISION_VALUE=14
++ eval 'echo $LIBFFI_VERSION'
+++ echo v3.2.1-alice1
+ VERSION_VALUE=v3.2.1-alice1
++ eval 'echo $LIBFFI_ROOT'
+++ echo /sw/slc9_x86-64/libffi/v3.2.1-alice1-14
+ ROOT_PATH_VALUE=/sw/slc9_x86-64/libffi/v3.2.1-alice1-14
+ '[' -z 14 ']'
+ echo 'bz2 FairCMakeModules defaults-release ninja safe_int date O2-customization CMake alibuild-recipe-tools double-conversion googlebenchmark UUID Alice-GRID-Utils MPFR json-c ninja-fortran pytorch_cpuinfo Python-modules-list'
+ tr '[:lower:]' '[:upper:]'
+ tr - _
+ tr ' ' '\n'
[0 more errors; see full log]

Full log here.