lavf/segment: Simplify CSV field quoting code

Should also be faster (though I doubt that hardly ever matters
for the usage here).

Also remove the pointer copy. Since we do not need to reset the
pointer to the start of the string, it is not needed anymore.
Signed-off-by: Alexander Strasser <eclipse7@gmx.net>

libavformat/segment.c

@@ -76,23 +76,15 @@ typedef struct {
 
 static void print_csv_escaped_str(AVIOContext *ctx, const char *str)
 {
-    const char *p;
-    int quote = 0;
-
-    /* check if input needs quoting */
-    for (p = str; *p; p++)
-        if (strchr("\",\n\r", *p)) {
-            quote = 1;
-            break;
-        }
+    int quote = !!str[strcspn(str, "\",\n\r")];
 
     if (quote)
         avio_w8(ctx, '"');
 
-    for (p = str; *p; p++) {
-        if (*p == '"')
+    for (; *str; str++) {
+        if (*str == '"')
             avio_w8(ctx, '"');
-        avio_w8(ctx, *p);
+        avio_w8(ctx, *str);
     }
     if (quote)
         avio_w8(ctx, '"');