MXS-1529 Prevent endless realloc loop

If the provided config path refers to a directory it can still
be opened and an attempt to read be made. However, as reading
will fail but end-of-file not be reached, we can't rely upon
'feof()' for detecting when to bail out.

As it is a user error to provide a directory as the config path,
that will be detected and deemed an error in a subsequent commit.

server/core/config.c

@@ -2448,7 +2448,7 @@ int maxscale_getline(char** dest, int* size, FILE* file)
     char* destptr = *dest;
     int offset = 0;
 
-    if (feof(file))
+    if (feof(file) || ferror(file))
     {
         return 0;
     }
@@ -2471,11 +2471,18 @@ int maxscale_getline(char** dest, int* size, FILE* file)
             }
         }
 
-        if ((destptr[offset] = fgetc(file)) == '\n' || feof(file))
+        int c = fgetc(file);
+
+        if ((c == '\n') || (c == EOF))
         {
             destptr[offset] = '\0';
             break;
         }
+        else
+        {
+            destptr[offset] = c;
+        }
+
         offset++;
     }