fix coverity complaint the right way

use an assert to document in a machine-readable form that the file is
expected to be null-terminated. this supersedes 5a58e962's approach of
appending a null char, which would just obfuscate a problem in the calling
code if it were to ever have an effect.

Change-Id: Iaedb575d20abb42d98e011949e792ecf4dde3e93
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/libs/utils/process_stub_unix.c

@@ -224,13 +224,13 @@ int main(int argc, char *argv[])
         fseek(envFd, 0, SEEK_END);
         size = ftell(envFd);
         rewind(envFd);
-        envdata = malloc(size + 1);
+        envdata = malloc(size);
         if (fread(envdata, 1, size, envFd) != (size_t)size) {
             perror("Failed to read env file");
             doExit(1);
         }
-        envdata[size] = '\0';
         fclose(envFd);
+        assert(!size || !envdata[size - 1]);
         for (count = 0, edp = envdata; edp < envdata + size; ++count)
             edp += strlen(edp) + 1;
         env = malloc((count + 2) * sizeof(char *));