Text: tighten up align*() internals with unreachable assertions.

There shouldn't be any other values passed to these. Compilers, don't
even attempt to say that the alignment value is now maybe uninitialized,
I'm watching you!

src/Magnum/Text/Renderer.cpp

@@ -195,7 +195,7 @@ Range2D alignRenderedLine(const Range2D& lineRectangle, const LayoutDirection di
     /** @todo this again assumes horizontal direction, needs to be updated once
         vertical (and possibly mixed horizontal/vertical) text is possible */
 
-    Float alignmentOffsetX = 0.0f;
+    Float alignmentOffsetX;
     if((UnsignedByte(alignment) & Implementation::AlignmentHorizontal) == Implementation::AlignmentLeft)
         alignmentOffsetX = -lineRectangle.left();
     else if((UnsignedByte(alignment) & Implementation::AlignmentHorizontal) == Implementation::AlignmentCenter) {
@@ -206,6 +206,7 @@ Range2D alignRenderedLine(const Range2D& lineRectangle, const LayoutDirection di
     }
     else if((UnsignedByte(alignment) & Implementation::AlignmentHorizontal) == Implementation::AlignmentRight)
         alignmentOffsetX = -lineRectangle.right();
+    else CORRADE_INTERNAL_ASSERT_UNREACHABLE(); /* LCOV_EXCL_LINE */
 
     /* Shift all positions */
     for(Vector2& i: positions)
@@ -224,8 +225,10 @@ Range2D alignRenderedBlock(const Range2D& blockRectangle, const LayoutDirection
     /** @todo this assumes vertical layout advance, needs to be updated once
         other directions are possible */
 
-    Float alignmentOffsetY = 0.0f;
-    if((UnsignedByte(alignment) & Implementation::AlignmentVertical) == Implementation::AlignmentBottom)
+    Float alignmentOffsetY;
+    if((UnsignedByte(alignment) & Implementation::AlignmentVertical) == Implementation::AlignmentLine)
+        alignmentOffsetY = 0.0f;
+    else if((UnsignedByte(alignment) & Implementation::AlignmentVertical) == Implementation::AlignmentBottom)
         alignmentOffsetY = -blockRectangle.bottom();
     else if((UnsignedByte(alignment) & Implementation::AlignmentVertical) == Implementation::AlignmentMiddle) {
         alignmentOffsetY = -blockRectangle.centerY();
@@ -235,6 +238,7 @@ Range2D alignRenderedBlock(const Range2D& blockRectangle, const LayoutDirection
     }
     else if((UnsignedByte(alignment) & Implementation::AlignmentVertical) == Implementation::AlignmentTop)
         alignmentOffsetY = -blockRectangle.top();
+    else CORRADE_INTERNAL_ASSERT_UNREACHABLE(); /* LCOV_EXCL_LINE */
 
     /* Shift all positions */
     for(Vector2& i: positions)