Fix function Classify::WriteIntTemplates (issue tesseract-ocr#3925)

It crashed when running mftraining because unicharset_size in file
"inttemp" was written with 8 bytes instead of 4 bytes.

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

# Conflicts:
#	src/classify/intproto.cpp

src/classify/intproto.cpp

@@ -954,7 +954,7 @@ void ClearFeatureSpaceWindow(NORM_METHOD norm_method, ScrollView *window) {
 void Classify::WriteIntTemplates(FILE *File, INT_TEMPLATES_STRUCT *Templates,
                                  const UNICHARSET &target_unicharset) {
   INT_CLASS_STRUCT *Class;
-  auto unicharset_size = target_unicharset.size();
+  uint32_t unicharset_size = target_unicharset.size();
   int version_id = -5; // When negated by the reader -1 becomes +1 etc.
 
   if (Templates->NumClasses != unicharset_size) {