Make jat__stat() more robust and clean

Revamp to make use of specific sub-routine that does not throw errors if
the key does not exist (zero messages/asserts yet) and also makes it
easier to sum up (assert count = PASS+FAIL count).

src/jat.sh.skel

     #
     local which=$1
     case $which in
-        swarc)  grep -cxF MESSAGE.WARNING "$(__jat__sd_path "llog")" ;;
-        pwarc)  grep -cxF MESSAGE.WARNING "$(__jat__sd_path "P.llog")" ;;
-        serrc)  grep -cxF MESSAGE.ERROR "$(__jat__sd_path "llog")" ;;
-        perrc)  grep -cxF MESSAGE.ERROR "$(__jat__sd_path "P.llog")" ;;
-        sfailc) grep -cxF ASSERT.FAIL "$(__jat__sd_path "vlog")" ;;
-        pfailc) grep -cxF ASSERT.FAIL "$(__jat__sd_path "P.vlog")" ;;
-        ppassc) grep -cxF ASSERT.PASS "$(__jat__sd_path "P.vlog")" ;;
-        spassc) grep -cxF ASSERT.PASS "$(__jat__sd_path "vlog")" ;;
-        pasrtc) grep -cx 'ASSERT.PASS\|ASSERT.FAIL' "$(__jat__sd_path "P.vlog")" ;;
-        sasrtc) grep -cx 'ASSERT.PASS\|ASSERT.FAIL' "$(__jat__sd_path "vlog")" ;;
+        swarc)  __jat__statcnt llog   MESSAGE.WARNING ;;
+        pwarc)  __jat__statcnt P.llog MESSAGE.WARNING ;;
+        serrc)  __jat__statcnt llog   MESSAGE.ERROR   ;;
+        perrc)  __jat__statcnt P.llog MESSAGE.ERROR   ;;
+        sfailc) __jat__statcnt vlog   ASSERT.FAIL ;;
+        pfailc) __jat__statcnt P.vlog ASSERT.FAIL ;;
+        ppassc) __jat__statcnt P.vlog ASSERT.PASS ;;
+        spassc) __jat__statcnt vlog   ASSERT.PASS ;;
+        pasrtc) __jat__statcnt P.vlog ASSERT.PASS ASSERT.FAIL ;;
+        sasrtc) __jat__statcnt vlog   ASSERT.PASS ASSERT.FAIL ;;
         *) __jat__usage "invalid statistic field: $which"
            return 2 ;;
     esac
     warn "jat.ERROR" "$1"
 }
 
+__jat__statcnt() {
+    #
+    # Sum up number of lines $2.. in session data key $1
+    #
+    # Print count of lines or 0 if the key is not present at all.
+    #
+    local key=$1; shift
+    local line
+    local sdpath
+    local sum=0
+    local lsum=0
+    sdpath=$(__jat__sd_path "$key")
+    test -f "$sdpath" || { echo 0; return 1; }
+    test -s "$sdpath" || { echo 0; return 1; }
+    for line in "$@"; do
+        lsum=$(grep -cxF "$line" "$sdpath")
+        sum=$((sum + lsum))
+    done
+    echo "$sum"
+    test "$sum" -gt 0
+}
+
 __jat__usage() {
     #
     # Print usage error $1 and hint according to FUNCNAME