Fix handling of single pages from multipage TIFF files (issue #2537)

That case now uses Leptonica to deliver the desired image instead of
using an inefficient loop in the Tesseract code.

See commit 54fafc4 which used similar
code in the past.

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

src/api/baseapi.cpp

@@ -1037,10 +1037,14 @@ bool TessBaseAPI::ProcessPagesMultipageTiff(const l_uint8 *data,
   int page = (tessedit_page_number >= 0) ? tessedit_page_number : 0;
   size_t offset = 0;
   for (; ; ++page) {
-    if (tessedit_page_number >= 0)
+    if (tessedit_page_number >= 0) {
       page = tessedit_page_number;
-    pix = (data) ? pixReadMemFromMultipageTiff(data, size, &offset)
-                 : pixReadFromMultipageTiff(filename, &offset);
+      pix = (data) ? pixReadMemTiff(data, size, page)
+                   : pixReadTiff(filename, page);
+    } else {
+      pix = (data) ? pixReadMemFromMultipageTiff(data, size, &offset)
+                   : pixReadFromMultipageTiff(filename, &offset);
+    }
     if (pix == nullptr) break;
     tprintf("Page %d\n", page + 1);
     char page_str[kMaxIntSize];