Windows: text/plain: check if already utf-8 before trying transcode

src/internfile/txtdcode.cpp

@@ -24,6 +24,10 @@
 #include "smallut.h"
 #include "listmem.h"
 
+#ifdef _WIN32
+#include "utf8iter.h"
+#endif
+
 using std::string;
 
 // Called after decoding from utf-8 failed. Handle the common case
@@ -111,6 +115,17 @@ bool RecollFilter::txtdcode(const string& who)
     int ecnt;
     string otext;
 
+#ifdef _WIN32
+    // Under Windows the environment charset will usually not be
+    // utf-8. We check if the text is actually utf-8. This is worth
+    // it, else the conversion from 8-bit is going to succeed if the
+    // text is already utf-8, and produce bogus data.
+    if (utf8check(itext, otext) >= 0) {
+        m_metaData[cstr_dj_keycharset] = cstr_utf8;
+        return true;
+    }
+#endif
+
     string bomfromcode = bomtocode(itext);
     if (!bomfromcode.empty()) {
         LOGDEB(who << "::txtdcode: " << " input charset changed from " <<