scanutils: Fix illegal memory access

Format strings which contain "%*s" show this error in Valgrind:

==32503== Conditional jump or move depends on uninitialised value(s)
==32503==    at 0x2B8BB0: tvfscanf(_IO_FILE*, char const*, __va_list_tag*) (scanutils.cpp:486)
==32503==    by 0x2B825A: tfscanf(_IO_FILE*, char const*, ...) (scanutils.cpp:234)
==32503==    by 0x272B01: read_unlv_file(STRING, int, int, BLOCK_LIST*) (blread.cpp:54)
==32503==    by 0x1753CD: tesseract::Tesseract::SegmentPage(STRING const*, BLOCK_LIST*, tesseract::Tesseract*, OSResults*) (pagesegmain.cpp:115)
==32503==    by 0x1363CD: tesseract::TessBaseAPI::FindLines() (baseapi.cpp:2291)
==32503==    by 0x130CF1: tesseract::TessBaseAPI::Recognize(ETEXT_DESC*) (baseapi.cpp:802)
==32503==    by 0x1322D3: tesseract::TessBaseAPI::ProcessPage(Pix*, int, char const*, char const*, int, tesseract::TessResultRenderer*) (baseapi.cpp:1176)
==32503==    by 0x131A84: tesseract::TessBaseAPI::ProcessPagesMultipageTiff(unsigned char const*, unsigned long, char const*, char const*, int, tesseract::TessResultRenderer*, int) (baseapi.cpp:1013)
==32503==    by 0x132052: tesseract::TessBaseAPI::ProcessPagesInternal(char const*, char const*, int, tesseract::TessResultRenderer*) (baseapi.cpp:1129)
==32503==    by 0x131B1E: tesseract::TessBaseAPI::ProcessPages(char const*, char const*, int, tesseract::TessResultRenderer*) (baseapi.cpp:1032)
==32503==    by 0x12E00C: main (tesseractmain.cpp:537)
==32503==  Uninitialised value was created by a stack allocation
==32503==    at 0x272A60: read_unlv_file(STRING, int, int, BLOCK_LIST*) (blread.cpp:41)

Signed-off-by: Stefan Weil <sw@weilnetz.de>

src/ccutil/scanutils.cpp

@@ -472,8 +472,10 @@ static int tvfscanf(FILE* stream, const char *format, va_list ap) {
 
             case 's':               // String
             {
-              char *sp;
-              sp = sarg = va_arg(ap, char *);
+              if (!(flags & FL_SPLAT)) {
+                sarg = va_arg(ap, char *);
+              }
+              char *sp = sarg;
               while (width--) {
                 q = fgetc(stream);
                 if (isspace(static_cast<unsigned char>(q)) || q <= 0) {
@@ -488,7 +490,6 @@ static int tvfscanf(FILE* stream, const char *format, va_list ap) {
               } else if (!(flags & FL_SPLAT)) {
                 *sp = '\0'; // Terminate output
                 converted++;
-              } else {
               }
             }
             break;