BufferGeometry: Workaround for computeTangents requiring a drawcall.

src/core/BufferGeometry.js

@@ -599,13 +599,19 @@ THREE.BufferGeometry.prototype = {
 		var j, jl;
 		var iA, iB, iC;
 
-		var offsets = this.offsets;
+		if ( this.drawcalls.length === 0 ) {
+
+			this.addDrawCall( 0, indices.length, 0 );
+
+		}
+
+		var drawcalls = this.drawcalls;
 
-		for ( j = 0, jl = offsets.length; j < jl; ++ j ) {
+		for ( j = 0, jl = drawcalls.length; j < jl; ++ j ) {
 
-			var start = offsets[ j ].start;
-			var count = offsets[ j ].count;
-			var index = offsets[ j ].index;
+			var start = drawcalls[ j ].start;
+			var count = drawcalls[ j ].count;
+			var index = drawcalls[ j ].index;
 
 			for ( i = start, il = start + count; i < il; i += 3 ) {
 
@@ -651,11 +657,11 @@ THREE.BufferGeometry.prototype = {
 
 		}
 
-		for ( j = 0, jl = offsets.length; j < jl; ++ j ) {
+		for ( j = 0, jl = drawcalls.length; j < jl; ++ j ) {
 
-			var start = offsets[ j ].start;
-			var count = offsets[ j ].count;
-			var index = offsets[ j ].index;
+			var start = drawcalls[ j ].start;
+			var count = drawcalls[ j ].count;
+			var index = drawcalls[ j ].index;
 
 			for ( i = start, il = start + count; i < il; i += 3 ) {