patch 8.1.0703: compiler warnings with 64-bit compiler

Problem:    Compiler warnings with 64-bit compiler.
Solution:   Change types, add type casts. (Mike Williams)
diff --git a/src/textprop.c b/src/textprop.c
index 8b7d3f1..389bd41 100644
--- a/src/textprop.c
+++ b/src/textprop.c
@@ -357,12 +357,12 @@
     static void
 set_text_props(linenr_T lnum, char_u *props, int len)
 {
-    char_u *text;
-    char_u *newtext;
-    size_t textlen;
+    char_u  *text;
+    char_u  *newtext;
+    int	    textlen;
 
     text = ml_get(lnum);
-    textlen = STRLEN(text) + 1;
+    textlen = (int)STRLEN(text) + 1;
     newtext = alloc(textlen + len);
     if (newtext == NULL)
 	return;