docproc: avoid segfault during file closing

In the function find_export_symbols, since the fopen file does not
exit when it fails, there is a dereference problem in fclose(fp),
which will cause a segmentation fault.

Signed-off-by: Yan Zhu <zhuyan2015@foxmail.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

scripts/basic/docproc.c

@@ -180,6 +180,7 @@ void find_export_symbols(char * filename)
 		{
 			fprintf(stderr, "docproc: ");
 			perror(real_filename);
+			exit(1);
 		}
 		while (fgets(line, MAXLINESZ, fp)) {
 			unsigned char *p;