vcap/rtsp: create fallback file in $TMPDIR

If running with Firejail, neither /tmp (used by tmpfile()) nor CWD may
be writable so try to create file in $TMPDIR (if defined, otherwise
there a default).

+ modified get_temp_file() opened file mode to be readable

src/utils/fs.c

@@ -149,7 +149,7 @@ FILE *get_temp_file(const char **filename) {
         static _Thread_local char filename_buf[MAX_PATH_SIZE];
 #ifdef _WIN32
         char *fname = tmpnam(filename_buf);
-        FILE *ret = fopen(fname, "wbx");
+        FILE *ret = fopen(fname, "w+bx");
         if (ret == NULL) {
                 return NULL;
         }
@@ -166,7 +166,7 @@ FILE *get_temp_file(const char **filename) {
         if (fd == -1) {
                 return NULL;
         };
-        FILE *ret = fdopen(fd, "wb");
+        FILE *ret = fdopen(fd, "w+b");
         if (ret == NULL) {
                 return NULL;
         }

src/video_capture/rtsp.c

@@ -72,6 +72,7 @@
 #include "rtp/rtpdec_state.h"
 #include "rtsp/rtsp_utils.h"
 #include "utils/color_out.h"       // for color_printf, TBOLD
+#include "utils/fs.h"              // for get_temp_file
 #include "utils/macros.h"          // for MIN, STR_LEN
 #include "utils/sdp.h"             // for get_video_codec_from_pt_rtpmap
 #include "utils/text.h" // base64_decode
@@ -845,7 +846,7 @@ init_rtsp(struct rtsp_state *s) {
     int port = s->vrtsp_state.port;
     FILE *sdp_file = tmpfile();
     if (sdp_file == NULL) {
-        sdp_file = fopen("rtsp.sdp", "w+");
+        sdp_file = get_temp_file(NULL);
         if (sdp_file == NULL) {
             perror("Creating SDP file");
             goto error;