Fix Casting error that occurred on certain GPUs (#2274)

Fix Casting error that occurred on certain GPUs

jme3-terrain/src/main/resources/Common/MatDefs/Terrain/AdvancedPBRTerrain.frag

@@ -259,7 +259,7 @@ void main(){
                     alphaBlend = alphaBlend_2;
                 }
 
-                texChannelForAlphaBlending = int(mod($i, 4.0)); //pick the correct channel (r g b or a) based on the layer's index
+                texChannelForAlphaBlending = int(mod(float($i), 4.0)); //pick the correct channel (r g b or a) based on the layer's index
                 switch(texChannelForAlphaBlending) {
                     case 0:
                         finalAlphaBlendForLayer = alphaBlend.r;

jme3-terrain/src/main/resources/Common/MatDefs/Terrain/PBRTerrain.frag

@@ -246,7 +246,7 @@ void main(){
                     alphaBlend = alphaBlend_2;
                 }
 
-                texChannelForAlphaBlending = int(mod($i, 4.0)); //pick the correct channel (r g b or a) based on the layer's index
+                texChannelForAlphaBlending = int(mod(float($i), 4.0)); //pick the correct channel (r g b or a) based on the layer's index
                 switch(texChannelForAlphaBlending) {
                     case 0:
                         finalAlphaBlendForLayer = alphaBlend.r;