parser_priv: Change type of fontdata_{size,used} to size_t

size_t is a more sensible type for as it is unsigned and accurately
represents the theoretical limits of object size. int may be larger or
smaller than size_t, which both would lead to problems and potential UB
with signed overflow.
There was no usage of negative values as error flags or similar and
those two fields are not part of the public API, so this change should
be safe.

To stay consistent, also adjust types of related variables in functions.

libass/ass.c

@@ -807,7 +807,7 @@ static int process_events_line(ASS_Track *track, char *str)
 }
 
 static unsigned char *decode_chars(const unsigned char *src,
-                                   unsigned char *dst, int cnt_in)
+                                   unsigned char *dst, size_t cnt_in)
 {
     uint32_t value = 0;
     for (int i = 0; i < cnt_in; i++)
@@ -825,9 +825,9 @@ static int decode_font(ASS_Track *track)
 {
     unsigned char *p;
     unsigned char *q;
-    int i;
-    int size;                   // original size
-    int dsize;                  // decoded size
+    size_t i;
+    size_t size;                   // original size
+    size_t dsize;                  // decoded size
     unsigned char *buf = 0;
 
     ass_msg(track->library, MSGL_V, "Font: %d bytes encoded data",
@@ -871,7 +871,7 @@ static int decode_font(ASS_Track *track)
 
 static int process_fonts_line(ASS_Track *track, char *str)
 {
-    int len;
+    size_t len;
 
     if (!strncmp(str, "fontname:", 9)) {
         char *p = str + 9;

libass/ass_priv.h

@@ -50,8 +50,8 @@ struct parser_priv {
     ParserState state;
     char *fontname;
     char *fontdata;
-    int fontdata_size;
-    int fontdata_used;
+    size_t fontdata_size;
+    size_t fontdata_used;
 
     // contains bitmap of ReadOrder IDs of all read events
     uint32_t *read_order_bitmap;