conf: require sourcedir files to be terminated by newline

When reading a *.sources file require that each line is termined by the
newline character to avoid processing an unfinished line, e.g. due to an
unexpected call of the reload command when the file is being written in
place.

conf.c

@@ -1694,8 +1694,9 @@ load_source_file(const char *filename)
     return;
 
   while (fgets(line, sizeof (line), f)) {
-    if (strlen(line) >= MAX_LINE_LENGTH)
-      continue;
+    /* Require lines to be terminated */
+    if (line[0] == '\0' || line[strlen(line) - 1] != '\n')
+      break;
 
     CPS_NormalizeLine(line);
     if (line[0] == '\0')