tools/acpixtract: handle AX_OPTIONAL_TABLES correctly

The previous commit introduced a regression while attempting to make
acpixtract not exit with -1 in case of a missing optional table.

Add an extra condition that checks that the number of detected instances
was 0 before checking AX_OPTIONAL_TABLES.

Fixes: ad5755d ("acpixtract: don't abort AxExtractTables for AX_OPTIONAL_TABLES")
Resolves: acpica#978
Signed-off-by: Daniil Tatianin <99danilt@gmail.com>

source/tools/acpixtract/acpixtract.c

@@ -213,7 +213,8 @@ AxExtractTables (
         AxNormalizeSignature (UpperSignature);
         Instances = AxCountTableInstances (InputPathname, UpperSignature);
 
-        if (Instances < MinimumInstances || MinimumInstances == AX_OPTIONAL_TABLES)
+        if (Instances < MinimumInstances ||
+            (Instances == 0 && MinimumInstances == AX_OPTIONAL_TABLES))
         {
             printf ("Table [%s] was not found in %s\n",
                 UpperSignature, InputPathname);