Handle malloc failures in emscripten_fetch_unpack_response_headers (#24043)

`emscripten_fetch_unpack_response_headers` now returns `NULL` when
`malloc` fails.

Author: stevenwdv

system/lib/fetch/emscripten_fetch.c

@@ -197,6 +197,9 @@ char **emscripten_fetch_unpack_response_headers(const char *headersString) {
     numHeaders++;
   }
   char **unpackedHeaders = (char**)malloc(sizeof(char*) * ((numHeaders * 2) + 1));
+  if (!unpackedHeaders) {
+    return NULL;
+  }
   unpackedHeaders[numHeaders * 2] = NULL;
 
   // Allocate each header.
@@ -206,17 +209,24 @@ char **emscripten_fetch_unpack_response_headers(const char *headersString) {
     const char *split = strchr(rowStart, ':');
     size_t headerSize = (size_t)split - (size_t)rowStart;
     char* header = (char*)malloc(headerSize + 1);
+    unpackedHeaders[headerNum] = header;
+    if (!header) {
+      emscripten_fetch_free_unpacked_response_headers(unpackedHeaders);
+      return NULL;
+    }
     strncpy(header, rowStart, headerSize);
     header[headerSize] = '\0';
 
     size_t valueSize = (size_t)rowEnd - (size_t)split;
     char* value = (char*)malloc(valueSize + 1);
+    unpackedHeaders[headerNum+1] = value;
+    if (!value) {
+      emscripten_fetch_free_unpacked_response_headers(unpackedHeaders);
+      return NULL;
+    }
     strncpy(value, split + 1, valueSize);
     value[valueSize] = '\0';
 
-    unpackedHeaders[headerNum] = header;
-    unpackedHeaders[headerNum+1] = value;
-
     rowStart = rowEnd + 1;
     rowEnd = strchr(rowStart, '\n');
   }