Return 1 as implicit alignment value.

Previously 0 was returned, which would fail at runtime for
division-by-zero in the following sanity check:

    CORRADE_INTERNAL_ASSERT(!(offset % BufferTexture::offsetAlignment()));

src/Magnum/Buffer.cpp

@@ -39,7 +39,7 @@ namespace Magnum {
 #ifndef MAGNUM_TARGET_GLES
 Int Buffer::minMapAlignment() {
     if(!Context::current()->isExtensionSupported<Extensions::GL::ARB::map_buffer_alignment>())
-        return 0;
+        return 1;
 
     GLint& value = Context::current()->state().buffer->minMapAlignment;
 
@@ -89,7 +89,7 @@ Int Buffer::shaderStorageOffsetAlignment() {
     #else
     if(!Context::current()->isVersionSupported(Version::GLES310))
     #endif
-        return 0;
+        return 1;
 
     GLint& value = Context::current()->state().buffer->shaderStorageOffsetAlignment;
 

src/Magnum/Buffer.h

@@ -441,7 +441,7 @@ class MAGNUM_EXPORT Buffer: public AbstractObject {
          *
          * The result is cached, repeated queries don't result in repeated
          * OpenGL calls. If extension @extension{ARB,map_buffer_alignment}
-         * (part of OpenGL 4.2) is not available, returns `0`.
+         * (part of OpenGL 4.2) is not available, returns `1`.
          * @see @ref map(), @fn_gl{Get} with @def_gl{MIN_MAP_BUFFER_ALIGNMENT}
          * @requires_gl No minimal value is specified for OpenGL ES.
          */
@@ -476,7 +476,7 @@ class MAGNUM_EXPORT Buffer: public AbstractObject {
          *
          * The result is cached, repeated queries don't result in repeated
          * OpenGL calls. If neither extension @extension{ARB,shader_storage_buffer_object}
-         * (part of OpenGL 4.3) nor OpenGL ES 3.1 is available, returns `0`.
+         * (part of OpenGL 4.3) nor OpenGL ES 3.1 is available, returns `1`.
          * @see @fn_gl{Get} with @def_gl{SHADER_STORAGE_BUFFER_OFFSET_ALIGNMENT}
          * @requires_gles30 Not defined in OpenGL ES 2.0
          */

src/Magnum/BufferTexture.cpp

@@ -49,7 +49,7 @@ Int BufferTexture::maxSize() {
 
 Int BufferTexture::offsetAlignment() {
     if(!Context::current()->isExtensionSupported<Extensions::GL::ARB::texture_buffer_range>())
-        return 0;
+        return 1;
 
     GLint& value = Context::current()->state().texture->bufferOffsetAlignment;
 

src/Magnum/BufferTexture.h

@@ -217,7 +217,7 @@ class MAGNUM_EXPORT BufferTexture: public AbstractTexture {
          *
          * The result is cached, repeated queries don't result in repeated
          * OpenGL calls. If extension @extension{ARB,texture_buffer_range}
-         * (part of OpenGL 4.3) is not available, returns `0`.
+         * (part of OpenGL 4.3) is not available, returns `1`.
          * @see @fn_gl{Get} with @def_gl{TEXTURE_BUFFER_OFFSET_ALIGNMENT}
          */
         static Int offsetAlignment();