fixed zero buffer bugs

src/main/java/bdv/jogl/VolumeRenderer/ShaderPrograms/ShaderSources/functions/accumulator/MaxCurvatureDifferenceAccumulator.java

@@ -100,8 +100,9 @@ public class MaxCurvatureDifferenceAccumulator extends AbstractVolumeAccumulator
 
 					//fill textures
 					FloatBuffer buffer = Buffers.newDirectFloatBuffer(container.valueMesh3d);
-					t.update(gl, 0, buffer, container.dimension);
-
+					if(buffer.capacity() > 0){
+						t.update(gl, 0, buffer, container.dimension);
+					}
 				}
 				this.needsUpdate.remove(key);
 			}

src/main/java/bdv/jogl/VolumeRenderer/ShaderPrograms/ShaderSources/functions/accumulator/SharpnessVolumeAccumulator.java

@@ -145,7 +145,9 @@ public class SharpnessVolumeAccumulator extends AbstractVolumeAccumulator {
 
 					//fill textures
 					FloatBuffer buffer = Buffers.newDirectFloatBuffer(container.valueMesh3d);
-					t.update(gl, 0, buffer, container.dimension);
+					if(buffer.capacity() > 0){
+						t.update(gl, 0, buffer, container.dimension);
+					}
 
 				}
 				this.needsUpdate.remove(key);