resolve syntactic ambiguity

Author: mohawk2

.github/workflows/ci.yml

@@ -13,7 +13,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-latest]
-        perl-version: ['5.10', '5.14', '5.20']
+        perl-version: ['5.16', '5.20']
         include:
           - perl-version: '5.30'
             os: ubuntu-latest

test.pl

@@ -1467,7 +1467,7 @@ sub cbResizeScene {
   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();
   my $fW = fH * $Width/$Height;
-  glFrustum(-$fW, $fW, -fH, fH, zNEAR, zFAR);
+  glFrustum(-$fW, $fW, -fH(), fH, zNEAR, zFAR);
   glMatrixMode(GL_MODELVIEW);
   $Window_Width  = $Width;
   $Window_Height = $Height;