ui-ssdiff: move LCS table away from the stack

Printing deferred line changes for files containing long lines would
cause a segfault.

- limit LCS table size: 128x128.
- move LCS table to global context: avoid allocating/freeing memory
  for every deferred line change.

Signed-off-by: Jamie Couture <jamie.couture@gmail.com>

ui-ssdiff.h

@@ -1,6 +1,18 @@
 #ifndef UI_SSDIFF_H
 #define UI_SSDIFF_H
 
+/*
+ * ssdiff line limits
+ */
+#ifndef MAX_SSDIFF_M
+#define MAX_SSDIFF_M 128
+#endif
+
+#ifndef MAX_SSDIFF_N
+#define MAX_SSDIFF_N 128
+#endif
+#define MAX_SSDIFF_SIZE ((MAX_SSDIFF_M) * (MAX_SSDIFF_N))
+
 extern void cgit_ssdiff_print_deferred_lines();
 
 extern void cgit_ssdiff_line_cb(char *line, int len);