patch 8.0.1687: 64 bit compiler warnings

Problem:    64 bit compiler warnings.
Solution:   change type, add type cast. (Mike Williams)
diff --git a/src/terminal.c b/src/terminal.c
index 7859941..9a62edd 100644
--- a/src/terminal.c
+++ b/src/terminal.c
@@ -3400,7 +3400,7 @@
     static void *
 vterm_malloc(size_t size, void *data UNUSED)
 {
-    return alloc_clear(size);
+    return alloc_clear((unsigned) size);
 }
 
     static void
@@ -4016,9 +4016,9 @@
     int	    fname_size;
     char_u  *p = fname;
     int	    i;
-    int	    off;
+    size_t  off;
 
-    textline = alloc(width + STRLEN(fname) + 1);
+    textline = alloc(width + (int)STRLEN(fname) + 1);
     if (textline == NULL)
 	return NULL;