curl: tool_read_cb fix of segfault

When transfers read client input without an upload file, the check if
upload file is '.' strcompared a NULL.

Add test 1548 to reproduce and verify fix.

Reported-by: d1r3ct0r
Fixes #17978
Closes #17987

src/tool_cb_rea.c

@@ -90,7 +90,7 @@ size_t tool_read_cb(char *buffer, size_t sz, size_t nmemb, void *userdata)
    Make sure we are in non-blocking mode and infd is not regular stdin
    On Linux per->infd should be stdin (0) and the block below should not
    execute */
-  if(!strcmp(per->uploadfile, ".") && per->infd > 0) {
+  if(per->uploadfile && !strcmp(per->uploadfile, ".") && per->infd > 0) {
 #if defined(_WIN32) && !defined(CURL_WINDOWS_UWP) && !defined(UNDER_CE)
     rc = recv(per->infd, buffer, curlx_uztosi(sz * nmemb), 0);
     if(rc < 0) {

tests/data/Makefile.am

@@ -203,7 +203,7 @@ test1516 test1517 test1518 test1519 test1520 test1521 test1522 test1523 \
 test1524 test1525 test1526 test1527 test1528 test1529 test1530 test1531 \
 test1532 test1533 test1534 test1535 test1536 test1537 test1538 test1539 \
 test1540 test1541 test1542 test1543 test1544 test1545 test1546 test1547 \
-\
+test1548 \
 test1550 test1551 test1552 test1553 test1554 test1555 test1556 test1557 \
 test1558 test1559 test1560 test1561 test1562 test1563 test1564 test1565 \
 test1566 test1567 test1568 test1569 test1570 test1571 test1572 test1573 \

tests/data/test1548

@@ -0,0 +1,43 @@
+<testcase>
+<info>
+<keywords>
+TELNET
+</keywords>
+</info>
+
+#
+# Server-side
+<reply>
+<data>
+</data>
+</reply>
+
+#
+# Client-side
+<client>
+<server>
+http
+</server>
+<features>
+telnet
+</features>
+<name>
+TELNET read stdin without upload file
+</name>
+<stdin>
+GET /we/want/%TESTNUMBER HTTP/1.0
+
+</stdin>
+<command>
+-m 1 telnet://%HOSTIP:%HTTPPORT
+</command>
+</client>
+
+#
+# Verify data after the test has been "shot"
+<verify>
+<errorcode>
+28
+</errorcode>
+</verify>
+</testcase>