If-then-else statements & correct line numbers

#KT-3036 Fixed

compiler/testData/codegen/statements/ifThenElse.kt

@@ -0,0 +1,9 @@
+fun z(b: Boolean) {}
+
+fun foo(b: Boolean) {
+    if (b) {
+        z(b)
+    } else {
+        z(b)
+    }
+}

compiler/testData/codegen/statements/ifThenElseEmpty.kt

@@ -0,0 +1,5 @@
+fun foo(b: Boolean) {
+    if (b) {
+    } else {
+    }
+}

compiler/testData/lineNumber/custom/ifThenElse.kt

@@ -0,0 +1,15 @@
+fun foo() {
+    if (0 < 1) {
+        System.out?.println()
+    } else {
+        System.out?.println()
+    }
+    
+    val b = if (1 < 2) {
+        System.out?.println()
+    } else {
+        System.out?.println()
+    }
+}
+
+// 2 3 5 8 9 11 8