7073913: The fix for 7017193 causes segfaults

Summary: Buffer overflow in os::get_line_chars
Reviewed-by: coleenp, dholmes, dcubed
Contributed-by: aph@redhat.com

src/share/vm/runtime/os.cpp

@@ -1299,7 +1299,7 @@ int os::get_line_chars(int fd, char* buf, const size_t bsize){
   size_t sz, i = 0;
 
   // read until EOF, EOL or buf is full
-  while ((sz = (int) read(fd, &buf[i], 1)) == 1 && i < (bsize-1) && buf[i] != '\n') {
+  while ((sz = (int) read(fd, &buf[i], 1)) == 1 && i < (bsize-2) && buf[i] != '\n') {
      ++i;
   }
 
@@ -1320,7 +1320,7 @@ int os::get_line_chars(int fd, char* buf, const size_t bsize){
   }
 
   // line is longer than size of buf, skip to EOL
-  int ch;
+  char ch;
   while (read(fd, &ch, 1) == 1 && ch != '\n') {
     // Do nothing
   }