easy: do not ignore poll() failures other than EINTR

RELEASE-NOTES

@@ -53,6 +53,7 @@ This release includes the following bugfixes:
  o docs: updates HTML index and general improvements
  o curlbuild.h.dist: enhance non-configure GCC ABI detection logic
  o sasl: Fixed null pointer reference when decoding empty digest challenge [8]
+ o easy: do not ignore poll() failures other than EINTR
 
 This release includes the following known bugs:
 

lib/easy.c

@@ -441,11 +441,19 @@ CURLcode curl_easy_perform(CURL *easy)
 
   while(!done && !mcode) {
     int still_running;
+    int ret;
 
-    mcode = curl_multi_wait(multi, NULL, 0, 1000, NULL);
+    mcode = curl_multi_wait(multi, NULL, 0, 1000, &ret);
+
+    if(mcode == CURLM_OK) {
+      if(ret == -1) {
+        /* poll() failed not on EINTR, indicate a network problem */
+        code = CURLE_RECV_ERROR;
+        break;
+      }
 
-    if(mcode == CURLM_OK)
       mcode = curl_multi_perform(multi, &still_running);
+    }
 
     /* only read 'still_running' if curl_multi_perform() return OK */
     if((mcode == CURLM_OK) && !still_running) {