Related tdf#172905: avoid magic number

Change-Id: I60c22d076f0c2435a07bfc12497499092dfb9d7d
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/208977
Reviewed-by: Julien Nabet <serval2412@yahoo.fr>
Tested-by: Jenkins

tools/source/stream/stream.cxx

@@ -838,6 +838,7 @@ void SvStream::DetectEncoding(size_t maxBytes)
 
     // by default, let's use the first character set detected
     const UCharsetMatch* match = matches[0];
+    constexpr int CONFIDENCE_MIN_SKIP_CHARSETS = 10;
     for (int i=0; i < matchCount; i++)
     {
         const char* pName = ucsdet_getName(matches[i], &uerr);
@@ -845,7 +846,7 @@ void SvStream::DetectEncoding(size_t maxBytes)
         SAL_INFO("tools.stream",
                 "\tcharacter set name=" << pName
                 << " has a confidence of " << confidence);
-        if (confidence == 10 &&
+        if (confidence == CONFIDENCE_MIN_SKIP_CHARSETS &&
              std::find(aSkipCharsets.begin(), aSkipCharsets.end(), pName) != aSkipCharsets.end())
         {
             continue;