Range filter: fixed duplicate charset.

If a proxied response had charset in Content-Type, the
charset was duplicated in a response to client request
with byte ranges.

src/http/modules/ngx_http_range_filter_module.c

diff --git a/src/http/modules/ngx_http_range_filter_module.c b/src/http/modules/ngx_http_range_filter_module.c
index 6143a87..bcc64fd 100644
--- a/src/http/modules/ngx_http_range_filter_module.c
+++ b/src/http/modules/ngx_http_range_filter_module.c
@@ -432,7 +432,9 @@
           + r->headers_out.content_type.len
           + sizeof(CRLF "Content-Range: bytes ") - 1;
 
-    if (r->headers_out.charset.len) {
+    if (r->headers_out.content_type_len == r->headers_out.content_type.len
+        && r->headers_out.charset.len)
+    {
         len += sizeof("; charset=") - 1 + r->headers_out.charset.len;
     }
 
@@ -451,7 +453,9 @@
      * "Content-Range: bytes "
      */
 
-    if (r->headers_out.charset.len) {
+    if (r->headers_out.content_type_len == r->headers_out.content_type.len
+        && r->headers_out.charset.len)
+    {
         ctx->boundary_header.len = ngx_sprintf(ctx->boundary_header.data,
                                            CRLF "--%0muA" CRLF
                                            "Content-Type: %V; charset=%V" CRLF
@@ -461,8 +465,6 @@
                                            &r->headers_out.charset)
                                    - ctx->boundary_header.data;
 
-        r->headers_out.charset.len = 0;
-
     } else if (r->headers_out.content_type.len) {
         ctx->boundary_header.len = ngx_sprintf(ctx->boundary_header.data,
                                            CRLF "--%0muA" CRLF
@@ -501,6 +503,8 @@
 
     r->headers_out.content_type_len = r->headers_out.content_type.len;
 
+    r->headers_out.charset.len = 0;
+
     /* the size of the last boundary CRLF "--0123456789--" CRLF */
 
     len = sizeof(CRLF "--") - 1 + NGX_ATOMIC_T_LEN + sizeof("--" CRLF) - 1;